1.
Time standard
–
A time standard is a specification for measuring time, either the rate at which time passes, or points in time, or both. In modern times, several time specifications have been recognized as standards. An example of a kind of time standard can be a time scale, a standard for civil time can specify both time intervals and time-of-day. Standardized time measurements are made using a clock to count periods of some cyclic change, historically, time standards were often based on the Earths rotational period. From the late 17th century to the 19th century it was assumed that the Earths daily rotational rate was constant. Time standards based on Earth rotation were replaced for use from 1952 onwards by an ephemeris time standard based on the Earths orbital period. Various types of second and day are used as the time interval for most time scales. Other intervals of time are usually defined in terms of these two, apparent solar time is based on the solar day, which is the period between one solar noon and the next. A solar day is approximately 24 hours of mean time, as the variation accumulates over a few weeks, there are differences as large as 16 minutes between apparent solar time and mean solar time. However, these cancel out over a year. There are also other perturbations such as Earths wobble, but these are less than a second per year, sidereal time is time by the stars. A sidereal rotation is the time it takes the Earth to make one revolution with respect to the stars and it is well known that observations of the Sun pose substantial obstacles to the achievement of accuracy in measurement. Mean solar time was originally apparent solar time corrected by the equation of time, Greenwich Mean Time was originally mean time deduced from meridian observations made at the Royal Greenwich Observatory. The principal meridian of that observatory was chosen in 1884 by the International Meridian Conference to be the Prime Meridian. GMT either by name or as mean time at Greenwich used to be an international time standard. The more current refined version of UT, UT1, is still in reality mean time at Greenwich, Greenwich Mean Time is still the legal time in the UK. But Coordinated Universal Time is in actual use in the UK. Universal Time is mean solar time at 0° longitude, some implementations are UT0 is the time of a particular place of observation
Time standard
–
Key concepts
2.
Greenwich Mean Time
–
Greenwich Mean Time is the mean solar time at the Royal Observatory in Greenwich, London. GMT was formerly used as the civil time standard, now superseded in that function by Coordinated Universal Time. Today GMT is considered equivalent to UTC for UK civil purposes and for navigation is considered equivalent to UT1, consequently, the term GMT should not be used for precise purposes. Due to Earths uneven speed in its orbit and its axial tilt, noon GMT is rarely the exact moment the sun crosses the Greenwich meridian. This event may occur up to 16 minutes before or after noon GMT, noon GMT is the annual average moment of this event, which accounts for the word mean in Greenwich Mean Time. Originally, astronomers considered a GMT day to start at noon while for almost everyone else it started at midnight, to avoid confusion, the name Universal Time was introduced to denote GMT as counted from midnight. Astronomers preferred the old convention to simplify their observational data, so each night was logged under a single calendar date. Today Universal Time usually refers to UTC or UT1, in some countries Greenwich Mean Time is the legal time in the winter and the population uses the term. For an explanation of why this is, see GMT in legislation below, synchronisation of the chronometer on GMT did not affect shipboard time, which was still solar time. Most time zones were based upon GMT, as an offset of a number of hours ahead of GMT or behind GMT and it was gradually adopted for other purposes, but a legal case in 1858 held local mean time to be the official time. On 14 May 1880, a signed by Clerk to Justices appeared in The Times, stating that Greenwich time is now kept almost throughout England. For example, our polling booths were opened, say, at 813 and closed at 413 PM. This was changed later in 1880, GMT was adopted on the Isle of Man in 1883, Jersey in 1898 and Guernsey in 1913. Ireland adopted GMT in 1916, supplanting Dublin Mean Time, hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924, rendering the time ball at the observatory redundant in the process. The daily rotation of the Earth is irregular and constantly slows, on 1 January 1972, GMT was superseded as the international civil time standard by Coordinated Universal Time, maintained by an ensemble of atomic clocks around the world. Indeed, even the Greenwich meridian itself is not quite what it used to be—defined by the centre of the instrument at the Observatory at Greenwich. Nevertheless, the line in the old observatorys courtyard today differs no more than a few metres from that line which is now the prime meridian of the world. Historically GMT has been used two different conventions for numbering hours. The long-standing astronomical convention dating from the work of Ptolemy, was to refer to noon as zero hours and this contrasted with the civil convention of referring to midnight as zero hours dating from the Romans
Greenwich Mean Time
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Greenwich clock with standard measurements
Greenwich Mean Time
–
light blue
Greenwich Mean Time
–
This arch that stretches over a
highway indicates the
prime meridian in
Spain.
3.
Mean solar time
–
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of time is the day. Two types of time are apparent solar time and mean solar time. Fix a tall pole vertically in the ground, at some instant on any day the shadow will point exactly north or south. That instant is local apparent noon,12,00 local apparent time, about 24 hours later the shadow will again point north/south, the Sun seeming to have covered a 360-degree arc around the Earths axis. When the Sun has covered exactly 15 degrees, local apparent time is 13,00 exactly, after 15 more degrees it will be 14,00 exactly. As explained in the equation of time article, this is due to the eccentricity of the Earths orbit, the effect of this is that a clock running at a constant rate – e. g. This is mean solar time, which is not perfectly constant from one century to the next but is close enough for most purposes. Currently a mean solar day is about 86,400.002 SI seconds, the two kinds of solar time are among the three kinds of time reckoning that were employed by astronomers until the 1950s. By the 1950s it had become clear that the Earths rotation rate was not constant, so astronomers developed ephemeris time, the apparent sun is the true sun as seen by an observer on Earth. Apparent solar time or true solar time is based on the apparent motion of the actual Sun and it is based on the apparent solar day, the interval between two successive returns of the Sun to the local meridian. Solar time can be measured by a sundial. The equivalent on other planets is termed local true solar time, the length of a solar day varies through the year, and the accumulated effect produces seasonal deviations of up to 16 minutes from the mean. The effect has two main causes, first, Earths orbit is an ellipse, not a circle, so the Earth moves faster when it is nearest the Sun and slower when it is farthest from the Sun. Second, due to Earths axial tilt, the Suns annual motion is along a circle that is tilted to Earths celestial equator. In June and December when the sun is farthest from the equator a given shift along the ecliptic corresponds to a large shift at the equator. So apparent solar days are shorter in March and September than in June or December and these lengths will change slightly in a few years and significantly in thousands of years. Mean solar time is the angle of the mean Sun plus 12 hours
Mean solar time
–
Sun and
Moon,
Nuremberg Chronicle, 1493
Mean solar time
Mean solar time
–
Key concepts
Mean solar time
–
Internal structure
4.
Prime meridian (Greenwich)
–
A prime meridian, based at the Royal Observatory, Greenwich, in London, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the meridian on their charts. In October of that year, at the behest of U. S. President Chester A. Arthur,41 delegates from 25 nations met in Washington, United States, for the International Meridian Conference. This conference selected the meridian passing through Greenwich as the prime meridian due to its popularity. However, France abstained from the vote, and French maps continued to use the Paris meridian for several decades, the prime meridian passes through the Airy transit circle of the Greenwich observatory. The actual reason for the discrepancy is that the strip is indeed at astronomical longitude zero degrees, zero minutes. Before the establishment of a meridian, most maritime countries established their own prime meridian. In 1721, Great Britain established its own meridian passing through a transit circle at the newly established Royal Observatory at Greenwich. The meridian was moved around 10 metres or so east on three occasions as transit circles with newer and better instruments were built, on each occasion next door to the existing one and this was to allow uninterrupted observation during each new construction. The final meridian was established as a line from the north pole to the south pole passing through the Airy transit circle. This became Great Britains meridian in 1851, for all practical purposes of the period, the changes as the meridian was moved went unnoticed. Transit instruments are installed to be perpendicular to the local level, in 1884, the International Meridian Conference took place to establish an internationally recognised single meridian. The meridian chosen was that which passed through the Airy transit circle at Greenwich, at around the time of this conference, scientists were making measurements to determine the deflection of the vertical on a large scale. The downward extended plumb lines dont even all intersect the axis of the Earth. To make computations feasible, scientists defined ellipsoids of revolution, a given ellipsoid would be a compromise for measurements in a given area. When the Airy transit circle was built, a basin was used to align the telescope to the perpendicular. While the local vertical defined at the Airy transit circle still points to the celestial meridian. As a result of this, the ITRF zero meridian, defined by a passing through the Earths rotation axis, is 102 metres to the east of the prime meridian
Prime meridian (Greenwich)
–
Tourists taking pictures with the Prime Meridian monument
Prime meridian (Greenwich)
–
Laser projected from the Royal Observatory in Greenwich marking the Prime meridian
Prime meridian (Greenwich)
–
A
GPS receiver at the prime meridian. This does not indicate a longitude of zero because the meridian is, in practice, 102 metres to the east.
5.
Coordinated Universal Time
–
Coordinated Universal Time, abbreviated to UTC, is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean time at 0° longitude. It is one of closely related successors to Greenwich Mean Time. For most purposes, UTC is considered interchangeable with GMT, the first Coordinated Universal Time was informally adopted on 1 January 1960. This change also adopted leap seconds to simplify future adjustments, a number of proposals have been made to replace UTC with a new system that would eliminate leap seconds, but no consensus has yet been reached. Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of universal time, see the Current number of leap seconds section for the number of leap seconds inserted to date. The official abbreviation for Coordinated Universal Time is UTC and this abbreviation arose from a desire by the International Telecommunication Union and the International Astronomical Union to use the same abbreviation in all languages. English speakers originally proposed CUT, while French speakers proposed TUC, the compromise that emerged was UTC, which conforms to the pattern for the abbreviations of the variants of Universal Time. Time zones around the world are expressed using positive or negative offsets from UTC, the westernmost time zone uses UTC−12, being twelve hours behind UTC, the easternmost time zone, theoretically, uses UTC+12, being twelve hours ahead of UTC. In 1995, the nation of Kiribati moved those of its atolls in the Line Islands from UTC-10 to UTC+14 so that the country would all be on the same day. UTC is used in internet and World Wide Web standards. The Network Time Protocol, designed to synchronise the clocks of computers over the internet, computer servers, online services and other entities that rely on having a universally accepted time use UTC as it is more specific than GMT. If only limited precision is needed, clients can obtain the current UTC from a number of official internet UTC servers, for sub-microsecond precision, clients can obtain the time from satellite signals. UTC is also the standard used in aviation, e. g. for flight plans. Weather forecasts and maps all use UTC to avoid confusion about time zones, the International Space Station also uses UTC as a time standard. Amateur radio operators often schedule their radio contacts in UTC, because transmissions on some frequencies can be picked up by many time zones, UTC is also used in digital tachographs used on large goods vehicles under EU and AETR rules. UTC divides time into days, hours, minutes and seconds, days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes, the number of seconds in a minute is usually 60, but with an occasional leap second, it may be 61 or 59 instead
Coordinated Universal Time
–
Key concepts
Coordinated Universal Time
–
World map of current time zones
6.
Star
–
It is primarily present in steroid-producing cells, including theca cells and luteal cells in the ovary, Leydig cells in the testis and cell types in the adrenal cortex. The aqueous phase between two membranes cannot be crossed by the lipophilic cholesterol, unless certain proteins assist in this process. It is now clear that this process is mediated by the action of StAR. The mechanism by which StAR causes cholesterol movement remains unclear as it appears to act from the outside of the mitochondria, some involve StAR transferring cholesterol itself like a shuttle. Another notion is that it causes cholesterol to be kicked out of the membrane to the inner. StAR may also promote the formation of contact sites between the outer and inner mitochondrial membranes to allow cholesterol influx, another suggests that StAR acts in conjunction with PBR, causing the movement of Cl− out of the mitochondria to facilitate contact site formation. However, evidence for an interaction between StAR and PBR remains elusive, in humans, the gene for StAR is located on chromosome 8p11.2 and the protein has 285 amino acids. The signal sequence of StAR that targets it to the mitochondria is clipped off in two steps with import into the mitochondria, phosphorylation at the serine at position 195 increases its activity. The domain of StAR important for promoting cholesterol transfer is the StAR-related transfer domain, StAR is the prototypic member of the START domain family of proteins and is thus also known as STARD1 for START domain-containing protein 1. It is hypothesized that the START domain forms a pocket in StAR that binds single cholesterol molecules for delivery to P450scc, the closest homolog to StAR is MLN64. Together they comprise the StarD1/D3 subfamily of START domain-containing proteins, StAR is a mitochondrial protein that is rapidly synthesized in response to stimulation of the cell to produce steroid. Hormones that stimulate its production depend on the type and include luteinizing hormone, ACTH. At the cellular level, StAR is synthesized typically in response to activation of the second messenger system. StAR has thus far found in all tissues that can produce steroids, including the adrenal cortex, the gonads, the brain. One known exception is the human placenta, mutations in the gene for StAR cause lipoid congenital adrenal hyperplasia, in which patients produce little steroid and can die shortly after birth. Mutations that less severely affect the function of StAR result in nonclassic lipoid CAH or familial glucocorticoid deficiency type 3, all known mutations disrupt StAR function by altering its START domain. In the case of StAR mutation, the phenotype does not present until birth since human placental steroidogenesis is independent of StAR. At the cellular level, the lack of StAR results in an accumulation of lipid within cells
Star
7.
Quasar
–
A quasar is an active galactic nucleus of very high luminosity. A quasar consists of a black hole surrounded by an orbiting accretion disk of gas. As gas in the accretion disk falls toward the black hole, quasars emit energy across the electromagnetic spectrum and can be observed at radio, infrared, visible, ultraviolet, and X-ray wavelengths. The most powerful quasars have luminosities exceeding 1041 W, thousands of greater than the luminosity of a large galaxy such as the Milky Way. Quasars are found over a broad range of distances. The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, as of 2011, the most distant known quasar is at redshift z=7.085, light observed from this quasar was emitted when the Universe was only 770 million years old. Because quasars are distant objects, any light which reaches the Earth is redshifted due to the expansion of space. In early optical images, quasars appeared as point sources, indistinguishable from stars, with infrared telescopes and the Hubble Space Telescope, the host galaxies surrounding the quasars have been detected in some cases. These galaxies are normally too dim to be seen against the glare of the quasar, most quasars, with the exception of 3C273 whose average apparent magnitude is 12.9, cannot be seen with small telescopes. The luminosity of some quasars changes rapidly in the optical range, because these changes occur very rapidly they define an upper limit on the volume of a quasar, quasars are not much larger than the Solar System. This implies a high power density. The mechanism of brightness changes probably involves relativistic beaming of astrophysical jets pointed nearly directly toward Earth, the highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth. Since light cannot escape the black holes, the energy is actually generated outside the event horizon by gravitational stresses. Central masses of 105 to 109 solar masses have been measured in quasars by using reverberation mapping. The matter accreting onto the hole is unlikely to fall directly in. Quasars may also be ignited or re-ignited when normal galaxies merge, in fact, it has been suggested that a quasar could form as the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3–5 billion years. More than 200,000 quasars are known, most from the Sloan Digital Sky Survey, all observed quasar spectra have redshifts between 0.056 and 7.085. Applying Hubbles law to these redshifts, it can be shown that they are between 600 million and 28.85 billion light-years away
Quasar
–
Artist's rendering of
ULAS J1120+0641, a very distant quasar powered by a black hole with a mass two billion times that of the Sun. Credit:
ESO /M. Kornmesser
Quasar
–
A
Hubble picture showing a quasar core
Quasar
–
Quasar QSO-160913+653228 is so distant its light has taken nine billion years to reach us, two thirds of the time that has elapsed since the
Big Bang.
Quasar
–
The
Chandra X-ray image is of the quasar PKS 1127-145, a highly luminous source of X-rays and visible light about 10 billion light years from Earth. An enormous X-ray jet extends at least a million light years from the quasar. Image is 60 arcsec on a side.
RA 11h 30m 7.10s
Dec -14° 49' 27" in Crater. Observation date: May 28, 2000. Instrument: ACIS.
8.
Solar time
–
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of time is the day. Two types of time are apparent solar time and mean solar time. Fix a tall pole vertically in the ground, at some instant on any day the shadow will point exactly north or south. That instant is local apparent noon,12,00 local apparent time, about 24 hours later the shadow will again point north/south, the Sun seeming to have covered a 360-degree arc around the Earths axis. When the Sun has covered exactly 15 degrees, local apparent time is 13,00 exactly, after 15 more degrees it will be 14,00 exactly. As explained in the equation of time article, this is due to the eccentricity of the Earths orbit, the effect of this is that a clock running at a constant rate – e. g. This is mean solar time, which is not perfectly constant from one century to the next but is close enough for most purposes. Currently a mean solar day is about 86,400.002 SI seconds, the two kinds of solar time are among the three kinds of time reckoning that were employed by astronomers until the 1950s. By the 1950s it had become clear that the Earths rotation rate was not constant, so astronomers developed ephemeris time, the apparent sun is the true sun as seen by an observer on Earth. Apparent solar time or true solar time is based on the apparent motion of the actual Sun and it is based on the apparent solar day, the interval between two successive returns of the Sun to the local meridian. Solar time can be measured by a sundial. The equivalent on other planets is termed local true solar time, the length of a solar day varies through the year, and the accumulated effect produces seasonal deviations of up to 16 minutes from the mean. The effect has two main causes, first, Earths orbit is an ellipse, not a circle, so the Earth moves faster when it is nearest the Sun and slower when it is farthest from the Sun. Second, due to Earths axial tilt, the Suns annual motion is along a circle that is tilted to Earths celestial equator. In June and December when the sun is farthest from the equator a given shift along the ecliptic corresponds to a large shift at the equator. So apparent solar days are shorter in March and September than in June or December and these lengths will change slightly in a few years and significantly in thousands of years. Mean solar time is the angle of the mean Sun plus 12 hours
Solar time
–
Sun and
Moon,
Nuremberg Chronicle, 1493
Solar time
Solar time
–
Key concepts
Solar time
–
Internal structure
9.
International Atomic Time
–
International Atomic Time is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earths geoid. It is the basis for Coordinated Universal Time, which is used for civil timekeeping all over the Earths surface, and for Terrestrial Time, as of 31 December 2016 when another leap second was added, TAI is exactly 37 seconds ahead of UTC. The 37 seconds results from the difference of 10 seconds at the start of 1972. TAI may be reported using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth, specifically, both Julian Dates and the Gregorian calendar are used. TAI in this form was synchronised with Universal Time at the beginning of 1958, TAI as a time scale is a weighted average of the time kept by over 400 atomic clocks in over 50 national laboratories worldwide. The clocks are compared using GPS signals and two-way satellite time, due to the signal averaging it is an order of magnitude more stable than its best clock alone would be. The majority of the clocks are caesium clocks, the definition of the SI second is written in terms of caesium, the participating institutions each broadcast, in real time, a frequency signal with timecodes, which is their estimate of TAI. Time codes are published in the form of UTC, which differs from TAI by a well-known integer number of seconds. These time scales are denoted in the form UTC in the UTC form, the TAI form may be denoted TAI. The latter is not to be confused with TA, which denotes an independent atomic time scale, the clocks at different institutions are regularly compared against each other. The International Bureau of Weights and Measures, combines these measurements to retrospectively calculate the average that forms the most stable time scale possible. This combined time scale is published monthly in Circular T, and is the canonical TAI and this time scale is expressed in the form of tables of differences UTC-UTC for each participating institution k. Errors in publication may be corrected by issuing a revision of the faulty Circular T or by errata in a subsequent Circular T, aside from this, once published in Circular T the TAI scale is not revised. In hindsight it is possible to discover errors in TAI, doing so does not create another version of TAI, it is instead considered to be creating a better realisation of Terrestrial Time. Early atomic time scales consisted of quartz clocks with frequencies calibrated by an atomic clock. Atomic timekeeping services started experimentally in 1955, using the first caesium atomic clock at the National Physical Laboratory, the Greenwich Atomic scale began in 1955 at the Royal Greenwich Observatory. The International Time Bureau began a time scale, Tm or AM, in July 1955, both the BIH scale and A.1 were defined by an epoch at the beginning of 1958, it was set to read Julian Date 2436204.5 at the corresponding UT2 instant. The procedures used by the BIH evolved, and the name for the time scale changed, A3 in 1963 and this synchronisation was inevitably imperfect, depending as it did on the astronomical realisation of UT2
International Atomic Time
–
Key concepts
10.
Leap second
–
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time in order to keep its time of day close to the mean solar time, or UT1. Without such a correction, time reckoned by Earths rotation drifts away from atomic time because of irregularities in the Earths rate of rotation. Since this system of correction was implemented in 1972,27 leap seconds have been inserted, like most time standards, UTC defines a grouping of seconds into minutes, hours, days, months, and years. However, the duration of one solar day is now slightly longer than 24 hours because the rotation of the Earth has slowed down. The purpose of a second is to compensate for this drift. Specifically, a leap second is inserted between second 23,59,59 of a chosen UTC calendar date and second 00,00,00 of the following date. All leap seconds have been scheduled for either June 30 or December 31, the extra second is displayed on UTC clocks as 23,59,60. On clocks that display local time tied to UTC, the second may be inserted at the end of some other hour. A negative leap second would suppress second 23,59,59 of the last day of a chosen month, since the introduction of leap seconds, the mean solar day has outpaced UTC only for very brief periods, and has not triggered a negative leap second. Because the Earths rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced, with this definition, the second was proposed in 1874 as the base unit of time in the CGS system of units. Because the tropical year was considered more fundamental than the year, in 1955. That value agreed to 1 part in 1010 with the second then in use. It was also close to 1⁄86400 of the solar day as averaged between years 1750 and 1892. However, for the past several centuries, the length of the solar day has been increasing by about 1. 4–1.7 ms per century. By 1961, the solar day was already a millisecond or two longer than 86,400 SI seconds. Thus, from 1961 to 1971, the rate of clocks was constantly slowed to remain synchronised with GMT. During that period, therefore, the seconds of broadcast services were actually longer than the SI second. By then, the UTC clock was already 10 seconds behind TAI, which had been synchronized with UT1 in 1958, but had been counting true SI seconds since then
Leap second
–
Key concepts
Leap second
–
Graph showing the difference between UT1 and UTC. Vertical segments correspond to leap seconds.
11.
Standard time
–
Historically, the concept was established during the 19th century to aid weather forecasting and train travel. Applied globally in the 20th century, the areas became extended around evenly spaced meridians into time zones which centered on them. The standard time set in time zone has come to be defined in terms of offsets from Universal Time. In regions where daylight saving time is used, that time is defined by another offset, during the 19th century, scheduled steamships and trains required time standardization in the industrialized world. A standardized time system was first used by British railways on December 1,1847, when they switched from local mean time and it was also given the name railway time reflecting the important role the railway companies played in bringing it about. The vast majority of Great Britains public clocks were standardized to GMT by 1855, until 1883 each United States railroad chose its own time standards. By 1870 the Allegheny Time service extended over 2,500 miles with 300 telegraph offices receiving time signals, in 1870 Charles F. Dowd proposed four time zones based on the meridian through Washington, DC for North American railroads. In 1872 he revised his proposal to base it on the Greenwich meridian, sandford Fleming, a Canadian, proposed worldwide Standard Time at a meeting of the Royal Canadian Institute on February 8,1879. Cleveland Abbe advocated standard time to coordinate international weather observations and resultant weather forecasts. In 1879 he recommended four time zones across the contiguous United States, william F. Allen, the Convention secretary, argued that North American railroads should adopt a five-zone standard, similar to the one in use today, to avoid government action. On October 11,1883, the heads of the major railroads met in Chicago at the Grand Pacific Hotel, although most railroads adopted the new system as scheduled, some did so early on October 7 and others late on December 2. S. /Canadian railroads in 1883. Standard time was not enacted into US law until the 1918 Standard Time Act established standard time in time zones, the daylight saving time portion of the law was repealed in 1919 over a presidential veto, but was reestablished nationally during World War II. In 1999, standard time was inducted into the North America Railway Hall of Fame in the category National, Technical Innovations, the Dominion of Newfoundland, whose capital St. In the Netherlands, introduction of the railways made it desirable to create a standard time, on 1 May 1909, Amsterdam Time or Dutch Time was introduced. Before that, time was measured in different cities and in the east of the country, in 1909, a national time was introduced which was the same as the local time in Amsterdam, to be precise the exact time of the Wester Tower. This time was indicated as GMT +0h 19m 32. 13s until 17 March 1937 and this time zone was also known as the Loenen time or Gorinchem time, as this was the exact time in both Loenen and Gorinchem. At noon in Amsterdam, it was 11,40 in London and 12,40 in Berlin, the shift to the current Central European Time zone took place on 16 May 1940. The German occupiers ordered the clock to be moved an hour and this time was kept in summer and winter throughout 1941 and 1942
Standard time
–
Telegraphic equipment used to transmit standard time from the
Allegheny Observatory
Standard time
–
Worldwide time zones at present
12.
Railroad
–
Rail transport is a means of conveyance of passengers and goods on wheeled vehicles running on rails, also known as tracks. It is also referred to as train transport. In contrast to road transport, where vehicles run on a flat surface. Tracks usually consist of rails, installed on ties and ballast, on which the rolling stock, usually fitted with metal wheels. Other variations are possible, such as slab track, where the rails are fastened to a concrete foundation resting on a prepared subsurface. Rolling stock in a transport system generally encounters lower frictional resistance than road vehicles, so passenger. The operation is carried out by a company, providing transport between train stations or freight customer facilities. Power is provided by locomotives which either draw electric power from a railway system or produce their own power. Most tracks are accompanied by a signalling system, Railways are a safe land transport system when compared to other forms of transport. The oldest, man-hauled railways date back to the 6th century BC, with Periander, one of the Seven Sages of Greece, Rail transport blossomed after the British development of the steam locomotive as a viable source of power in the 19th centuries. With steam engines, one could construct mainline railways, which were a key component of the Industrial Revolution, also, railways reduced the costs of shipping, and allowed for fewer lost goods, compared with water transport, which faced occasional sinking of ships. The change from canals to railways allowed for markets in which prices varied very little from city to city. In the 1880s, electrified trains were introduced, and also the first tramways, starting during the 1940s, the non-electrified railways in most countries had their steam locomotives replaced by diesel-electric locomotives, with the process being almost complete by 2000. During the 1960s, electrified high-speed railway systems were introduced in Japan, other forms of guided ground transport outside the traditional railway definitions, such as monorail or maglev, have been tried but have seen limited use. The history of the growth, decline and restoration to use of transport can be divided up into several discrete periods defined by the principal means of motive power used. The earliest evidence of a railway was a 6-kilometre Diolkos wagonway, trucks pushed by slaves ran in grooves in limestone, which provided the track element. The Diolkos operated for over 600 years, Railways began reappearing in Europe after the Dark Ages. The earliest known record of a railway in Europe from this period is a window in the Minster of Freiburg im Breisgau in Germany
Railroad
–
Four
BNSF GE C44-9W diesel locomotives hauling a mixed freight train along the banks of the
Columbia River, between
Kennewick and
Wishram,
Washington State, United States
Railroad
–
Horsecar in
Brno, Czech Republic
Railroad
–
A British steam locomotive-hauled train
Railroad
–
Tren a las Nubes (Train to the Clouds), located in
Salta,
Argentina
13.
Clock
–
A clock is an instrument to measure, keep, and indicate time. The word clock is derived from the Celtic words clagan and clocca meaning bell, a silent instrument missing such a striking mechanism has traditionally been known as a timepiece. In general usage today a clock refers to any device for measuring and displaying the time, Watches and other timepieces that can be carried on ones person are often distinguished from clocks. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units, the day, the lunar month. Devices operating on several physical processes have been used over the millennia, a sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, an example being the hourglass. Water clocks, along with the sundials, are possibly the oldest time-measuring instruments, spring-driven clocks appeared during the 15th century. During the 15th and 16th centuries, clockmaking flourished, the next development in accuracy occurred after 1656 with the invention of the pendulum clock. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation, the electric clock was patented in 1840. The development of electronics in the 20th century led to clocks with no clockwork parts at all, the timekeeping element in every modern clock is a harmonic oscillator, a physical object that vibrates or oscillates at a particular frequency. This object can be a pendulum, a fork, a quartz crystal. Analog clocks usually indicate time using angles, Digital clocks display a numeric representation of time. Two numeric display formats are used on digital clocks, 24-hour notation. Most digital clocks use electronic mechanisms and LCD, LED, or VFD displays, for convenience, distance, telephony or blindness, auditory clocks present the time as sounds. There are also clocks for the blind that have displays that can be read by using the sense of touch, some of these are similar to normal analog displays, but are constructed so the hands can be felt without damaging them. The evolution of the technology of clocks continues today, the study of timekeeping is known as horology. The apparent position of the Sun in the sky moves over the course of a day, shadows cast by stationary objects move correspondingly, so their positions can be used to indicate the time of day. A sundial shows the time by displaying the position of a shadow on a flat surface, sundials can be horizontal, vertical, or in other orientations
Clock
–
The
Swiss railway clock.
Clock
–
The
Shepherd gate clock at the
Royal Observatory, Greenwich.
Clock
–
Simple horizontal sundial.
Clock
–
The flow of
sand in an
hourglass can be used to keep track of elapsed time.
14.
Train
–
A train is a form of rail transport consisting of a series of vehicles that usually runs along a rail track to transport cargo or passengers. Motive power is provided by a locomotive or individual motors in self-propelled multiple units. Although historically steam propulsion dominated, the most common forms are diesel and electric locomotives. Other energy sources include horses, engine or water-driven rope or wire winch, gravity, pneumatics, batteries, the word train comes from the Old French trahiner, from the Latin trahere pull, draw. There are various types of trains that are designed for particular purposes, a train may consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit. The first trains were rope-hauled, gravity powered or pulled by horses, from the early 19th century almost all were powered by steam locomotives. A passenger train is one which includes passenger-carrying vehicles which can often be very long, one notable and growing long-distance train category is high-speed rail. In order to much faster operation over 500 km/h, innovative Maglev technology has been researched for years. In most countries, such as the United Kingdom, the distinction between a tramway and a railway is precise and defined in law, a freight train uses freight cars to transport goods or materials. Freight and passengers may be carried in the train in a mixed consist. Rail cars and machinery used for maintenance and repair of tracks, etc. are termed maintenance of way equipment, similarly, dedicated trains may be used to provide support services to stations along a train line, such as garbage or revenue collection. There are various types of trains that are designed for particular purposes, a train can consist of a combination of one or more locomotives and attached railroad cars, or a self-propelled multiple unit. Trains can also be hauled by horses, pulled by a cable, special kinds of trains running on corresponding special railways are atmospheric railways, monorails, high-speed railways, maglev, rubber-tired underground, funicular and cog railways. A passenger train may consist of one or several locomotives and coaches, alternatively, a train may consist entirely of passenger carrying coaches, some or all of which are powered as a multiple unit. In many parts of the world, particularly the Far East and Europe, freight trains are composed of wagons or trucks rather than carriages, though some parcel and mail trains are outwardly more like passenger trains. Trains can also be mixed, comprising both passenger accommodation and freight vehicles, special trains are also used for track maintenance, in some places, this is called maintenance of way. A train with a locomotive attached at each end is described as top and tailed, where a second locomotive is attached temporarily to assist a train up steep banks or grades it is referred to as banking in the UK, or helper service in North America. Recently, many loaded trains in the United States have been made up one or more locomotives in the middle or at the rear of the train
Train
–
A
BNSF intermodal freight train passes through
Wisconsin, United States
Train
–
Steam locomotive -hauled passenger train
Train
–
British Rail Class 390 Electric multiple unit train
Train
–
A
Transperth B-series train
15.
Marine chronometer
–
A marine chronometer is a timepiece that is precise and accurate enough to be used as a portable time standard, it can therefore be used to determine longitude by means of celestial navigation. Timepieces made in Switzerland may display the word chronometer only if certified by the COSC, to determine a position on the Earths surface, it is necessary and sufficient to know the latitude, longitude, and altitude. Altitude considerations can, of course, be ignored for vessels operating at sea level, until the mid-1750s, accurate navigation at sea out of sight of land was an unsolved problem due to the difficulty in calculating longitude. Navigators could determine their latitude by measuring the angle at noon or, in the Northern Hemisphere. To find their longitude, however, they needed a standard that would work aboard a ship. Observation of regular celestial motions, such as Galileos method based on observing Jupiters natural satellites, was not possible at sea due to the ships motion. The lunar distances method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer, the Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530. The purpose of a chronometer is to measure accurately the time of a fixed location. This is particularly important for navigation, knowing GMT at local noon allows a navigator to use the time difference between the ships position and the Greenwich Meridian to determine the ships longitude. The creation of a timepiece which would work reliably at sea was difficult, christiaan Huygens, following his invention of the pendulum clock in 1656, made the first attempt at a marine chronometer in 1673 in France, under the sponsorship of Jean-Baptiste Colbert. He obtained a patent for his invention from Colbert, but his clock remained imprecise at sea, the first published use of the term was in 1684 in Arcanum Navarchicum, a theoretical work by Kiel professor Matthias Wasmuth. This was followed by a theoretical description of a chronometer in works published by English scientist William Derham in 1713. Attempts to construct a marine chronometer were begun by Jeremy Thacker in England in 1714. In 1714, the British government offered a prize for a method of determining longitude at sea. His first two sea timepieces H1 and H2 used this system, but he realised that they had a sensitivity to centrifugal force. However, H3s circular balances still proved too inaccurate and he abandoned the large machines. Harrison solved the problems with his much smaller H4 chronometer design in 1761. H4 looked much like a large five-inch diameter pocket watch, in 1761, Harrison submitted H4 for the £20,000 longitude prize
Marine chronometer
–
Breguet twin barrel box chronometer.
Marine chronometer
–
The marine "Chronometer" of
Jeremy Thacker used
gimbals and a
vacuum in a bell jar.
Marine chronometer
–
Henry Sully (1680-1729) presented a first marine chronometer in 1716.
Marine chronometer
–
John Harrison 's H1 marine chronometer of 1735.
16.
Telegraphy
–
Telegraphy is the long-distance transmission of textual or symbolic messages without the physical exchange of an object bearing the message. Thus semaphore is a method of telegraphy, whereas pigeon post is not, telegraphy requires that the method used for encoding the message be known to both sender and receiver. Such methods are designed according to the limits of the medium used. The use of signals, beacons, reflected light signals. In the 19th century, the harnessing of electricity led to the invention of electrical telegraphy, the advent of radio in the early 20th century brought about radiotelegraphy and other forms of wireless telegraphy. The word telegraph was first coined by the French inventor of the Semaphore line, Claude Chappe, a telegraph is a device for transmitting and receiving messages over long distances, i. e. for telegraphy. The word telegraph alone now generally refers to an electrical telegraph, Wireless telegraphy is also known as CW, for continuous wave, as opposed to the earlier radio technique of using a spark gap. Contrary to the definition used by Chappe, Morse argued that the term telegraph can strictly be applied only to systems that transmit. This is to be distinguished from semaphore, which transmits messages. Smoke signals, for instance, are to be considered semaphore, according to Morse, telegraph dates only from 1832 when Pavel Schilling invented one of the earliest electrical telegraphs. A telegraph message sent by a telegraph operator or telegrapher using Morse code was known as a telegram. A cablegram was a sent by a submarine telegraph cable. Later, a Telex was a sent by a Telex network. A wire picture or wire photo was a picture that was sent from a remote location by a facsimile telegraph. A diplomatic telegram, also known as a cable, is the term given to a confidential communication between a diplomatic mission and the foreign ministry of its parent country. These continue to be called telegrams or cables regardless of the used for transmission. Commercial electrical telegraphs were introduced from 1837, the first telegraphs came in the form of optical telegraph, including the use of smoke signals, beacons, or reflected light, which have existed since ancient times. Early proposals for a telegraph system were made to the Royal Society by Robert Hooke in 1684 and were first implemented on an experimental level by Sir Richard Lovell Edgeworth in 1767
Telegraphy
–
Replica of
Claude Chappe 's optical telegraph on the Litermont near
Nalbach, Germany
Telegraphy
–
Demonstration of the semaphore
Telegraphy
–
Pavel Schilling, an early pioneer of electrical telegraphy
Telegraphy
–
Cooke and Wheatstone's five-needle, six-wire telegraph
17.
Sandford Fleming
–
Sir Sandford Fleming, KCMG was a Scottish Canadian engineer and inventor. Born and raised in Scotland, he emigrated to colonial Canada at the age of 18, in 1827, Fleming was born in Kirkcaldy, Fife, Scotland to Andrew and Elizabeth Fleming. At the age of 14 he was apprenticed as a surveyor and in 1845, at the age of 18, he emigrated with his older brother David to colonial Canada. Their route took them through many cities of the Canadian colonies, Quebec City, Montreal and he qualified as a surveyor in Canada in 1849. In 1849 he created the Royal Canadian Institute with several friends, although initially intended as a professional institute for surveyors and engineers it became a more general scientific society. In 1851 he designed the Threepenny Beaver, the first Canadian postage stamp, throughout this time he was fully employed as a surveyor, mostly for the Grand Trunk Railway. Fleming served in the 10th Battalion Volunteer Rifles of Canada and was appointed to the rank of captain on January 1,1862 and he retired from the militia in 1865. As soon as he arrived in Peterborough, Ontario in 1845, Fleming became friendly with the family of his wife, the Halls. However, it was not until an accident almost ten years later that the young people’s love for each other was revealed. A year after this incident, in January 1855, Sandford married Ann Jane Hall and they were to have nine children of whom two died young. The oldest son, Frank Andrew, accompanied Fleming in his great Western expedition of 1872, the Fleming and Hall families saw each other often. Starting as assistant engineer in 1852, Fleming replaced Cumberland in 1855 but was in turn ousted by him in 1862, in 1863 he became the chief government surveyor of Nova Scotia charged with the construction of a line from Truro to Pictou. In 1862 he placed before the government a plan for a railway connecting the Atlantic and Pacific oceans. In 1867 he was appointed engineer-in-chief of the Intercolonial Railway which became a federal project and his insistence on building the bridges of iron and stone instead of wood was controversial at the time, but was soon vindicated by their resistance to fire. By 1871, the strategy of a connection was being used to bring British Columbia into federation. One of his companions, George Monro Grant wrote an account of the trip, which became a best-seller. By 1880, with 600 miles completed, a change of government brought a desire for a company to own the whole project and Fleming was dismissed by Sir Charles Tupper. It was the hardest blow of Flemings life, though he obtained a promise of monopoly, later revoked, on his next project, nevertheless, in 1884 he became a director of the Canadian Pacific Railway and was present as the last spike was driven
Sandford Fleming
–
Portrait of Sir Sandford Fleming by
John Wycliffe Lowes Forster
Sandford Fleming
–
Fleming with his grandchildren in 1893
Sandford Fleming
–
Sandford Fleming (in tallest hat) at the ceremony of the "last spike" being driven on the Canadian Pacific Railway
Sandford Fleming
–
Fleming Memorial Plaque: "Inventor of Standard Time", War Memorial Gardens, Kirkcaldy, Fife, Scotland
18.
Royal Greenwich Observatory
–
The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park, overlooking the River Thames. It played a role in the history of astronomy and navigation. The observatory was commissioned in 1675 by King Charles II, with the stone being laid on 10 August. The site was chosen by Sir Christopher Wren and he appointed John Flamsteed as the first Astronomer Royal. The building was completed in the summer of 1676, the building was often called Flamsteed House, in reference to its first occupant. The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century,1675 –22 June, Royal Observatory founded. 1675 –10 August, construction began,1714 Longitude Act established the Board of Longitude and Longitude rewards. The Astronomer Royal was, until the Board was dissolved in 1828,1767 Astronomer Royal Nevil Maskelyne began publication of the Nautical Almanac, based on observations made at the Observatory. 1833 Daily time signals began, marked by dropping a Time ball,1899 The New Physical Observatory was completed. 1924 Hourly time signals from the Royal Observatory were first broadcast on 5 February,1948 Office of the Astronomer Royal was moved to Herstmonceux. 1957 Royal Observatory completed its move to Herstmonceux, becoming the Royal Greenwich Observatory, the Greenwich site is renamed the Old Royal Observatory. Greenwich site is returned to its name, the Royal Observatory. The Ordnance Office was given responsibility for building the Observatory, with Moore providing the key instruments, Moore donated two clocks, built by Thomas Tompion, which were installed in the 20 foot high Octagon Room, the principal room of the building. They were of unusual design, each with a pendulum 13 feet in length mounted above the face, giving a period of four seconds. British astronomers have used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments, subsequently, nations across the world used it as their standard for mapping and timekeeping. When the Airy circle became the reference for the meridian, the difference resulting from the change was considered enough to be neglected. When a new triangulation was done between 1936 and 1962, scientists determined that in the Ordnance Survey system the longitude of the international Greenwich meridian was not 0° and this old astronomical prime meridian has been replaced by a more precise prime meridian
Royal Greenwich Observatory
–
Royal Observatory, Greenwich. A
time ball sits atop the Octagon Room.
Royal Greenwich Observatory
–
Flamsteed House in 1824
Royal Greenwich Observatory
–
Royal Observatory, Greenwich c. 1902 as depicted on a postcard
Royal Greenwich Observatory
–
Former Royal Greenwich Observatory,
Herstmonceux, East Sussex
19.
International Meridian Conference
–
The International Meridian Conference was a conference held in October 1884 in Washington, D. C. in the United States, to determine a prime meridian for international use. The conference was held at the request of U. S. President Chester A. Arthur, the subject to discuss was the choice of a meridian to be employed as a common zero of longitude and standard of time reckoning throughout the world. It resulted in selection of the Greenwich Meridian as the standard for zero degrees longitude. By the 1870s there was both to establish a prime meridian for worldwide navigation purposes and to unify local times for railway timetables. In Britain, the Great Western Railway had standardised time by 1840, the Post Office was by this time transmitting time signals from Greenwich by telegraph to most parts of the country to set the clocks. In the United States, the problems were more severe. This envisaged clocks showing 24-hour universal time with an extra dial having a local time rounded to the nearest hour and he also pointed out that many of the corrections for local mean time were greater than those involved in abandoning solar time. In 1878/9, he produced modified proposals using the Greenwich meridian, flemings two papers were considered so important that in June 1879 the British Government forwarded copies to eighteen foreign countries and to various scientific bodies in England. At the same time the American Metrological Society produced a Report on Standard Time by Cleveland Abbe, the Naval Observatory had also foiled the onward transmission of the Greenwich time signal from Harvard, where it was received via transatlantic cable and used to time a signal ball in Boston. The Seventh International Geodesic Conference in Rome in October 1883 then thrashed out most of the technical details and that from this meridian longitude shall be counted in two directions up to 180 degrees, east longitude being plus and west longitude minus. That the Conference expresses the hope that as soon as may be practicable the astronomical and nautical days will be arranged everywhere to begin at midnight, resolution 2, fixing the meridian at Greenwich, was passed 22–1, France and Brazil abstained. The French did not adopt the Greenwich meridian until 1911, resolution 4 expressly exempts standard time from the universal day. Thus the conference did not adopt any time zones, contrary to popular belief, regarding resolution 6, Great Britain had already shifted the beginning of the nautical day from noon, twelve hours before midnight, to midnight in 1805, during the Battle of Trafalgar. The astronomical day was shifted from noon, twelve hours after midnight, the following resolutions were not adopted, On 13 Oct, Resolved, That the initial meridian should have a character of absolute neutrality. It should be chosen exclusively so as to secure to science and to international commerce all possible advantages, - Twenty-one noes and three ayes. - France, Brazil, San Domingo voted in favor, in the end, the pragmatic argument for continuity with most nautical charts won the day and the French delegation abstained in the vote. There was discussion of setting zones as small as 10 minutes, most European countries aligned their clocks with Greenwich within ten years, Sweden and North America already having done so, and the trend continued. Greenwich Time and the discovery of the longitude, Proceedings of the 1884 International Meridian Conference - notes with links to scanned page images at Steve Allens site Fleming, Sandford
International Meridian Conference
–
Local times across the United States, major towns
International Meridian Conference
–
The vertical red line left of the middle is the
Greenwich meridian.
20.
Nautical chart
–
A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Nautical charts are essential tools for marine navigation, many countries require vessels, especially commercial ships, Nautical charting may take the form of charts printed on paper or computerized electronic navigational charts. With each daily download, critical data such as Local Notice to Mariners is added to the on-demand chart files so that these charts will be up to date at the time of printing, Nautical charts are based on hydrographic surveys. As surveying is laborious and time-consuming, hydrographic data for many areas of sea may be dated, depths are measured in a variety of ways. Historically the sounding line was used, in modern times, echo sounding is used for measuring the seabed in the open sea. When measuring the depth of water over an entire obstruction, such as a shipwreck. This ensures that difficult to find projections, such as masts, Nautical charts are issued by power of the national hydrographic offices in many countries. These charts are considered official in contrast to those made by commercial publishers, many hydrographic offices provide regular, sometimes weekly, manual updates of their charts through their sales agents. Individual hydrographic offices produce national chart series and international chart series, there are also commercially published charts, some of which may carry additional information of particular interest, e. g. for yacht skippers. The nature of a waterway depicted by a chart may change, therefore, old or uncorrected charts should never be used for navigation. Every producer of nautical charts also provides a system to inform mariners of changes that affect the chart. In the U. S. NOAA also has a partner who prints the POD NOAA charts. To give notice to mariners, radio broadcasts provide advance notice of urgent corrections, a good way to keep track of corrections is with a Chart and Publication Correction Record Card system. When the time comes to use the chart, he pulls the chart and charts card and this system ensures that every chart is properly corrected prior to use. A prudent mariner should obtain a new chart if he has not kept track of corrections, various Digital Notices to Mariners systems are available on the market such as Digitrace, Voyager, or ChartCo, to correct British Admiralty charts as well as NOAA charts. These systems provide only vessel relevant corrections via e-mail or web downloads, tracings to assist corrections are provided at the same time. The Canadian Coast Guard produces the Notice to Mariners publication which informs mariners of important navigational safety matters affecting Canadian Waters and this electronic publication is published on a monthly basis and can be downloaded from the Notices to Mariners Web site. The information in the Notice to Mariners is formatted to simplify the correction of paper charts, various and diverse methods exist for the correction of electronic navigational charts
Nautical chart
–
A pre-Mercator nautical chart of 1571, from Portuguese cartographer
Fernão Vaz Dourado (c. 1520–c.1580). It belongs to the so-called plane chart model, where observed latitudes and magnetic directions are plotted directly into the plane, with a constant scale, as if the Earth's surface were a flat plane (Portuguese National Archives of Torre do Tombo, Lisbon)
Nautical chart
–
A nautical chart of the
Warnemünde harbor shown on
OpenSeaMap
Nautical chart
–
Automatically labeled nautical chart
21.
Map
–
A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. Many maps are static, fixed to paper or some other durable medium, although the earliest maps known are of the heavens, geographic maps of territory have a very long tradition and exist from ancient times. The word map comes from the medieval Latin Mappa mundi, wherein mappa meant napkin or cloth, thus, map became the shortened term referring to a two-dimensional representation of the surface of the world. Cartography or map-making is the study and practice of crafting representations of the Earth upon a flat surface, in addition to location information maps may also be used to portray contour lines indicating constant values of elevation, temperature, rainfall, etc. The orientation of a map is the relationship between the directions on the map and the compass directions in reality. The word orient is derived from Latin oriens, meaning East, in the Middle Ages many maps, including the T and O maps, were drawn with East at the top. Today, the most common – but far from universal – cartographic convention is that North is at the top of a map, several kinds of maps are often traditionally not oriented with North at the top, Maps from non-Western traditions are oriented a variety of ways. Old maps of Edo show the Japanese imperial palace as the top, labels on the map are oriented in such a way that you cannot read them properly unless you put the imperial palace above your head. Medieval European T and O maps such as the Hereford Mappa Mundi were centred on Jerusalem with East at the top, indeed, prior to the reintroduction of Ptolemys Geography to Europe around 1400, there was no single convention in the West. Portolan charts, for example, are oriented to the shores they describe, Maps of cities bordering a sea are often conventionally oriented with the sea at the top. Route and channel maps have traditionally been oriented to the road or waterway they describe, polar maps of the Arctic or Antarctic regions are conventionally centred on the pole, the direction North would be towards or away from the centre of the map, respectively. Typical maps of the Arctic have 0° meridian towards the bottom of the page, reversed maps, also known as Upside-Down maps or South-Up maps, reverse the North is up convention and have south at the top. Buckminster Fullers Dymaxion maps are based on a projection of the Earths sphere onto an icosahedron, the resulting triangular pieces may be arranged in any order or orientation. Modern digital GIS maps such as ArcMap typically project north at the top of the map, compass decimal degrees can be converted to math degrees by subtracting them from 450, if the answer is greater than 360, subtract 360. The scale statement may be taken as exact when the region mapped is small enough for the curvature of the Earth to be neglected, over larger regions where the curvature cannot be ignored we must use map projections from the curved surface of the Earth to the plane. Thus for map projections we must introduce the concept of point scale, which is a function of position, although the scale statement is nominal it is usually accurate enough for all but the most precise of measurements. Large scale maps, say 1,10,000, cover relatively small regions in detail and small scale maps, say 1,10,000,000, cover large regions such as nations, continents. The large/small terminology arose from the practice of writing scales as numerical fractions, there is no exact dividing line between large and small but 1/100,000 might well be considered as a medium scale
Map
–
World map (2004,
CIA World Factbook)
Map
–
World map (1689,
Amsterdam)
Map
–
A celestial map from the 17th century, by the cartographer
Frederik de Wit
Map
–
The
Hereford Mappa Mundi from about 1300,
Hereford Cathedral, England, is a classic "T-O" map with Jerusalem at centre, east toward the top, Europe the bottom left and Africa on the right.
22.
International Astronomical Union
–
The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II
International Astronomical Union
–
International Astronomical Union
23.
Civil time
–
In modern usage, civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks. UTC is calculated by reference to atomic clocks, and was adopted in 1972, in traditional astronomical usage, civil time was mean solar time reckoned from midnight. Before 1925, the astronomical time 00,00,00 meant noon, in 1928, the International Astronomical Union introduced the term Universal Time for GMT beginning at midnight, but the two Nautical Almanac Offices did not accept it until 1952. Category, Time by country Category, Time zones Time Scales
Civil time
–
Key concepts
24.
Sun
–
The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
Sun
–
The Sun in visible wavelength with filtered white light on 8 July 2014. Characteristic
limb darkening and numerous
sunspots are visible.
Sun
–
During a total
solar eclipse, the solar
corona can be seen with the naked eye, during the brief period of totality.
Sun
–
Taken by
Hinode 's Solar Optical Telescope on 12 January 2007, this image of the Sun reveals the filamentary nature of the plasma connecting regions of different magnetic polarity.
Sun
–
Visible light photograph of sunspot, 13 December 2006
25.
Very Long Baseline Interferometry
–
Very-long-baseline interferometry is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from a radio source, such as a quasar, is collected at multiple radio telescopes on Earth. The distance between the telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, Data received at each antenna in the array include arrival times from a local atomic clock, such as a hydrogen maser. At a later time, the data are correlated with data from other antennas that recorded the same radio signal, the resolution achievable using interferometry is proportional to the observing frequency. VLBI is most well known for imaging distant cosmic radio sources, spacecraft tracking, using VLBI in this manner requires large numbers of time difference measurements from distant sources observed with a global network of antennas over a period of time. Some of the results derived from VLBI include, High resolution radio imaging of cosmic radio sources. Variations in the Earths orientation and length of day, the most sensitive VLBI array in the world is the European VLBI Network. This is an array which brings together the largest European radiotelescopes for typically week-long sessions. The combination of the EVN and VLBA is known as Global VLBI, VLBI has traditionally operated by recording the signal at each telescope on magnetic tapes or disks, and shipping those to the correlation center for replay. Recently, it has become possible to connect VLBI radio telescopes in close to real-time, while employing the local time references of the VLBI technique. The image to the shows the first science produced by the European VLBI Network using e-VLBI. The data from 6 telescopes were processed in time at the European Data Processing centre at JIVE. The Netherlands Academic Research Network SURFnet provides 6 x 1 Gbit/s connectivity between JIVE and the GEANT2 network, in the quest for even greater angular resolution, dedicated VLBI satellites have been placed in Earth orbit to provide greatly extended baselines. Experiments incorporating such space-borne array elements are termed Space Very Long Baseline Interferometry, another space VLBI mission, Spektr-R, was launched in July 2011. In VLBI interferometry, the digitized antenna data are recorded at each of the telescopes. The antenna signal is sampled with a precise and stable atomic clock that is additionally locked onto a GPS time standard. Alongside the astronomical data samples, the output of this clock is recorded on the tape/disk media, the recorded media are then transported to a central location
Very Long Baseline Interferometry
–
Some of the
Atacama Large Millimeter Array radio telescopes.
Very Long Baseline Interferometry
–
The eight radio telescopes of the Smithsonian
Submillimeter Array, located at the
Mauna Kea Observatory in Hawai'i.
Very Long Baseline Interferometry
26.
International Telecommunication Union
–
ITU, based in Geneva, Switzerland, is a member of the United Nations Development Group. ITU has been an intergovernmental public-private partnership organization since its inception, ITU was formed in 1865, in Paris, at the International Telegraph Convention, this makes it one of the oldest intergovernmental organizations in the world. ITU became a United Nations specialized agency in 1947, the ITU comprises three sectors, each managing a different aspect of the matters handled by the Union, as well as ITU Telecom. The sectors were created during the restructuring of ITU at its 1992 Plenipotentiary Conference, radiocommunication Established in 1927 as the International Radio Consultative Committee or CCIR, this sector manages the international radio-frequency spectrum and satellite orbit resources. In 1992, the CCIR became the ITU-R, Standardization Standardization was the original purpose of ITU since its inception. Established in 1956 as the International Telephone and Telegraph Consultative Committee or CCITT, in 1993, the CCITT became the ITU-T. Development Established in 1992, this sector helps spread equitable, sustainable and affordable access to information and communication technologies, ITU Telecom ITU Telecom organizes major events for the worlds ICT community. A permanent General Secretariat, headed by the Secretary General, manages the work of the Union. The basic texts of the ITU are adopted by the ITU Plenipotentiary Conference, the ITU is headed by a Secretary-General, who is elected to a four-year term by the member states at the ITU Plenipotentiary Conference. On 23 October 2014 Houlin Zhao was elected 19th Secretary-General of the ITU at the Plenipotentiary Conference in Busan and his four-year mandate started on 1 January 2015, and he was formally inaugurated on 15 January 2015. There are 193 Member States of the ITU, which are all UN member states, the most recent member state to join the ITU is South Sudan, which became a member on 14 July 2011. The Republic of China was blocked from membership by the Peoples Republic of China, palestine was admitted as an observer in 2010. The Summit was held as two conferences in 2003 and 2005 in Geneva and Tunis, respectively, with the aim of bridging the digital divide, in December 2012, the ITU facilitated The World Conference on International Telecommunications 2012 in Dubai. WCIT-12 was a conference to address International Telecommunications Regulations, the international rules for telecommunications. The previous conference to update the Regulations was held in Melbourne in 1988, in August 2012, ITU called for a public consultation on a draft document ahead of the conference. Telecommunications ministers from 193 countries attended the conference in Dubai, the current regulatory structure was based on voice telecommunications, when the Internet was still in its infancy. In 1988, telecommunications operated under regulated monopolies in most countries, as the Internet has grown, organizations such as ICANN have come into existence to manage key resources such as Internet addresses and Domain Names. Some outside the United States believe that the United States exerts too much influence over the governance of the Internet, current proposals look to take into account the prevalence of data communications
International Telecommunication Union
International Telecommunication Union
–
International Telecommunication Union
International Telecommunication Union
–
International Telecommunication Union – anniversary 125 years. Post of USSR, 1990.
27.
Tidal acceleration
–
Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite, and the primary planet that it orbits. The acceleration causes a gradual recession of a satellite in a prograde orbit away from the primary, the process eventually leads to tidal locking, usually of the smaller first, and later the larger body. The Earth–Moon system is the best studied case, the similar process of tidal deceleration occurs for satellites that have an orbital period that is shorter than the primarys rotational period, or that orbit in a retrograde direction. The naming is somewhat confusing, because the speed of the relative to the body it orbits is decreased as a result of tidal acceleration. Laplaces initial computation accounted for the effect, thus seeming to tie up the theory neatly with both modern and ancient observations. It took some time for the community to accept the reality. But eventually it became clear that three effects are involved, when measured in terms of solar time. Beside the effects of changes in Earths orbital eccentricity, as found by Laplace and corrected by Adams. First there is a real retardation of the Moons angular rate of orbital motion and this increases the Moons angular momentum around Earth. Secondly there is an apparent increase in the Moons angular rate of orbital motion and this arises from Earths loss of angular momentum and the consequent increase in length of day. Because the Moons mass is a fraction of that of Earth. The mass of the Moon is sufficiently large, and it is sufficiently close, in particular, the water of the oceans bulges out towards and away from the Moon. The average tidal bulge is synchronized with the Moons orbit, however, Earths rotation drags the position of the tidal bulge ahead of the position directly under the Moon. As a consequence, there exists a substantial amount of mass in the bulge that is offset from the line through the centers of Earth and the Moon. Because of this offset, a portion of the pull between Earths tidal bulges and the Moon is not perpendicular to the Earth–Moon line, i. e. there exists a torque between Earth and the Moon. This boosts the Moon in its orbit, and slows the rotation of Earth, as a result of this process, the mean solar day, which is nominally 86,400 seconds long, is actually getting longer when measured in SI seconds with stable atomic clocks. The small difference accumulates over time, which leads to a difference between our clock time on the one hand, and Atomic Time and Ephemeris Time on the other hand. This led to the introduction of the second in 1972 to compensate for differences in the bases for time standardization
Tidal acceleration
–
A picture of the
Earth and the
Moon from
Mars. The presence of the moon (which has about 1/81 the mass of Earth), is slowing Earth's rotation and lengthening the day by about 2 ms every century.
28.
Moon
–
The Moon is an astronomical body that orbits planet Earth, being Earths only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, following Jupiters satellite Io, the Moon is second-densest satellite among those whose densities are known. The average distance of the Moon from the Earth is 384,400 km, the Moon is thought to have formed about 4.51 billion years ago, not long after Earth. It is the second-brightest regularly visible celestial object in Earths sky, after the Sun and its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art. The Moons gravitational influence produces the ocean tides, body tides, and this matching of apparent visual size will not continue in the far future. The Moons linear distance from Earth is currently increasing at a rate of 3.82 ±0.07 centimetres per year, since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft. The usual English proper name for Earths natural satellite is the Moon, the noun moon is derived from moone, which developed from mone, which is derived from Old English mōna, which ultimately stems from Proto-Germanic *mǣnōn, like all Germanic language cognates. Occasionally, the name Luna is used, in literature, especially science fiction, Luna is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon. The principal modern English adjective pertaining to the Moon is lunar, a less common adjective is selenic, derived from the Ancient Greek Selene, from which is derived the prefix seleno-. Both the Greek Selene and the Roman goddess Diana were alternatively called Cynthia, the names Luna, Cynthia, and Selene are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana is connected to dies meaning day, several mechanisms have been proposed for the Moons formation 4.51 billion years ago, and some 60 million years after the origin of the Solar System. These hypotheses also cannot account for the angular momentum of the Earth–Moon system. This hypothesis, although not perfect, perhaps best explains the evidence, eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists, You have eighteen months. Go back to your Apollo data, go back to computer, do whatever you have to. Dont come to our conference unless you have something to say about the Moons birth, at the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular. Afterward there were only two groups, the giant impact camp and the agnostics. Giant impacts are thought to have been common in the early Solar System, computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth–Moon system
Moon
–
Full moon as seen from Earth's
northern hemisphere
Moon
–
The Moon, tinted reddish, during a
lunar eclipse
Moon
–
Near side of the Moon
Moon
–
Far side of the Moon
29.
Mean solar day
–
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of time is the day. Two types of time are apparent solar time and mean solar time. Fix a tall pole vertically in the ground, at some instant on any day the shadow will point exactly north or south. That instant is local apparent noon,12,00 local apparent time, about 24 hours later the shadow will again point north/south, the Sun seeming to have covered a 360-degree arc around the Earths axis. When the Sun has covered exactly 15 degrees, local apparent time is 13,00 exactly, after 15 more degrees it will be 14,00 exactly. As explained in the equation of time article, this is due to the eccentricity of the Earths orbit, the effect of this is that a clock running at a constant rate – e. g. This is mean solar time, which is not perfectly constant from one century to the next but is close enough for most purposes. Currently a mean solar day is about 86,400.002 SI seconds, the two kinds of solar time are among the three kinds of time reckoning that were employed by astronomers until the 1950s. By the 1950s it had become clear that the Earths rotation rate was not constant, so astronomers developed ephemeris time, the apparent sun is the true sun as seen by an observer on Earth. Apparent solar time or true solar time is based on the apparent motion of the actual Sun and it is based on the apparent solar day, the interval between two successive returns of the Sun to the local meridian. Solar time can be measured by a sundial. The equivalent on other planets is termed local true solar time, the length of a solar day varies through the year, and the accumulated effect produces seasonal deviations of up to 16 minutes from the mean. The effect has two main causes, first, Earths orbit is an ellipse, not a circle, so the Earth moves faster when it is nearest the Sun and slower when it is farthest from the Sun. Second, due to Earths axial tilt, the Suns annual motion is along a circle that is tilted to Earths celestial equator. In June and December when the sun is farthest from the equator a given shift along the ecliptic corresponds to a large shift at the equator. So apparent solar days are shorter in March and September than in June or December and these lengths will change slightly in a few years and significantly in thousands of years. Mean solar time is the angle of the mean Sun plus 12 hours
Mean solar day
–
Sun and
Moon,
Nuremberg Chronicle, 1493
Mean solar day
Mean solar day
–
Key concepts
Mean solar day
–
Internal structure
30.
Planet
–
The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye and these were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, in 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of mass based on where or what they orbit. The planets were thought by Ptolemy to orbit Earth in deferent, at about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the planets share characteristics such as volcanism, hurricanes, tectonics. Planets are generally divided into two types, large low-density giant planets, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System, in order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, several thousands of planets around other stars have been discovered in the Milky Way. e. in the habitable zone. On December 20,2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way, around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include not only in the Solar System. The ambiguities inherent in defining planets have led to much scientific controversy, the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the fixed stars, ancient Greeks called these lights πλάνητες ἀστέρες or simply πλανῆται, from which todays word planet was derived. In ancient Greece, China, Babylon, and indeed all pre-modern civilizations, it was almost universally believed that Earth was the center of the Universe and that all the planets circled Earth. The first civilization known to have a theory of the planets were the Babylonians
Planet
Planet
Planet
Planet
31.
Radar
–
Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the objects location and speed. Radar was developed secretly for military use by several nations in the period before, the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging. The term radar has since entered English and other languages as a common noun, high tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Other systems similar to make use of other parts of the electromagnetic spectrum. One example is lidar, which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves, as early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, an instructor at the Imperial Russian Navy school in Kronstadt. The next year, he added a spark-gap transmitter, in 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, the German inventor Christian Hülsmeyer was the first to use radio waves to detect the presence of distant metallic objects. In 1904, he demonstrated the feasibility of detecting a ship in dense fog and he obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23,1904 for a radar system. It operated on a 50 cm wavelength and the radar signal was created via a spark-gap. In 1915, Robert Watson-Watt used radio technology to advance warning to airmen. Watson-Watt became an expert on the use of direction finding as part of his lightning experiments. As part of ongoing experiments, he asked the new boy, Arnold Frederic Wilkins, Wilkins made an extensive study of available units before selecting a receiver model from the General Post Office. Its instruction manual noted that there was fading when aircraft flew by, in 1922, A. Hoyt Taylor and Leo C. Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, eight years later, Lawrence A. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war. Hugon, began developing a radio apparatus, a part of which was installed on the liner Normandie in 1935
Radar
–
Long-range radar
antenna, used to track space objects and ballistic missiles.
Radar
–
Radar of the type used for detection of aircraft. It rotates steadily, sweeping the airspace with a narrow beam.
Radar
–
Experimental radar antenna, US
Naval Research Laboratory, Anacostia, D. C., late 1930s
Radar
–
A
Chain Home tower in Great Baddow, United Kingdom
32.
General relativity
–
General relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newtons law of gravitation, providing a unified description of gravity as a geometric property of space and time. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter, the relation is specified by the Einstein field equations, a system of partial differential equations. Examples of such differences include gravitational time dilation, gravitational lensing, the redshift of light. The predictions of relativity have been confirmed in all observations. Although general relativity is not the only theory of gravity. Einsteins theory has important astrophysical implications, for example, it implies the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. The bending of light by gravity can lead to the phenomenon of gravitational lensing, General relativity also predicts the existence of gravitational waves, which have since been observed directly by physics collaboration LIGO. In addition, general relativity is the basis of current cosmological models of an expanding universe. Soon after publishing the special theory of relativity in 1905, Einstein started thinking about how to incorporate gravity into his new relativistic framework. In 1907, beginning with a thought experiment involving an observer in free fall. After numerous detours and false starts, his work culminated in the presentation to the Prussian Academy of Science in November 1915 of what are now known as the Einstein field equations. These equations specify how the geometry of space and time is influenced by whatever matter and radiation are present, the Einstein field equations are nonlinear and very difficult to solve. Einstein used approximation methods in working out initial predictions of the theory, but as early as 1916, the astrophysicist Karl Schwarzschild found the first non-trivial exact solution to the Einstein field equations, the Schwarzschild metric. This solution laid the groundwork for the description of the stages of gravitational collapse. In 1917, Einstein applied his theory to the universe as a whole, in line with contemporary thinking, he assumed a static universe, adding a new parameter to his original field equations—the cosmological constant—to match that observational presumption. By 1929, however, the work of Hubble and others had shown that our universe is expanding and this is readily described by the expanding cosmological solutions found by Friedmann in 1922, which do not require a cosmological constant. Lemaître used these solutions to formulate the earliest version of the Big Bang models, in which our universe has evolved from an extremely hot, Einstein later declared the cosmological constant the biggest blunder of his life
General relativity
–
A simulated
black hole of 10
solar masses within the
Milky Way, seen from a distance of 600 kilometers.
General relativity
–
Albert Einstein developed the theories of special and general relativity. Picture from 1921.
General relativity
–
Einstein cross: four images of the same astronomical object, produced by a
gravitational lens
General relativity
–
Artist's impression of the space-borne gravitational wave detector
LISA
33.
Polar motion
–
Polar motion of the Earth is the motion of the Earths rotational axis relative to its crust. This is measured with respect to a frame in which the solid Earth is fixed. This variation is only a few meters, polar motion is defined relative to a conventionally defined reference axis, the CIO, being the poles average location over the year 1900. The mean displacement far exceeds the magnitude of the wobbles, the latter are determined based on the International Terrestrial Reference System, which follows the polar motion. e. The slow rise of land that was formerly burdened with ice sheets or glaciers, the drift is roughly along the 80th meridian west. However, since about year 2000, the pole has found new direction of drift and this dramatic eastward shift in drift direction is attributed to the global scale mass transport between the oceans and the continents. Major earthquakes cause abrupt polar motion by altering the distribution of the Earths solid mass. These shifts, however, are small in magnitude relative to the long-term core/mantle. In the absence of external torques, the vector of the angular momentum M of a system remains constant and is directed toward a fixed point in space. In the case of the Earth, it is almost identical with its axis of rotation, the vector of the figure axis F of the system wobbles around M. This motion is called Eulers free nutation, for a rigid Earth which is an oblate spheroid to a good approximation, the figure axis F is its geometric axis defined by the geographic north and south pole. It is identical with the axis of its moment of inertia. The observed angle between M and F is a few hundred milliarcseconds which gives rise to a displacement of several meters between the figure axis of the Earth and its angular momentum. This is the polar motion. This observed free nutation is called Chandler wobble, there exist, in addition, polar motions with smaller periods of the order of decades. Finally, a secular polar drift of about 0, the annual variation was discovered by Karl Friedrich Küstner in 1885 by exact measurements of the variation of the latitude of stars, while S. C. Chandler found the free nutation in 1891. Both periods superpose, giving rise to a frequency with a period of about 5 to 8 years. They are also called nutations, except for the slowest, which is the precession of the equinoxes, polar motion is observed routinely by very-long-baseline interferometry, lunar laser ranging and satellite laser ranging
Polar motion
–
Figure 2. Displacement vector m of the annual component of polar motion as function of year. Numbers and tick marks indicate the beginning of each calendar month. The dash-dotted line is in the direction of the major axis. The line in the direction of the minor axis is the location of the excitation function vs. time of year. (100 mas (milliarcseconds) = 3.09 m on the Earth's surface)
Polar motion
–
Polar motion in arc seconds as function of time in days (0.1 arcsec ≈ 3 meters). [
citation needed]
34.
Global Positioning System
–
The Global Positioning System is a space-based radionavigation system owned by the United States government and operated by the United States Air Force. The GPS system operates independently of any telephonic or internet reception, the GPS system provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, however, the US government can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War. The U. S. Department of Defense developed the system and it became fully operational in 1995. Roger L. Easton of the Naval Research Laboratory, Ivan A, getting of The Aerospace Corporation, and Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes, in 2000, the U. S. Congress authorized the modernization effort, GPS III. In addition to GPS, other systems are in use or under development, mainly because of a denial of access. The Russian Global Navigation Satellite System was developed contemporaneously with GPS, GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more quickly and accurately, to within two meters. There are also the European Union Galileo positioning system and Chinas BeiDou Navigation Satellite System, special and general relativity predict that the clocks on the GPS satellites would be seen by the Earths observers to run 38 microseconds faster per day than the clocks on the Earth. The GPS calculated positions would quickly drift into error, accumulating to 10 kilometers per day, the relativistic time effect of the GPS clocks running faster than the clocks on earth was corrected for in the design of GPS. The Soviet Union launched the first man-made satellite, Sputnik 1, two American physicists, William Guier and George Weiffenbach, at Johns Hopkinss Applied Physics Laboratory, decided to monitor Sputniks radio transmissions. Within hours they realized that, because of the Doppler effect, the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the users location and this led them and APL to develop the TRANSIT system. In 1959, ARPA also played a role in TRANSIT, the first satellite navigation system, TRANSIT, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour, in 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS. In the 1970s, the ground-based OMEGA navigation system, based on comparison of signal transmission from pairs of stations. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy, during the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded and it is also the reason for the ultra secrecy at that time
Global Positioning System
–
Artist's conception of GPS Block II-F satellite in Earth orbit.
Global Positioning System
–
Geodesy
Global Positioning System
–
Civilian GPS receivers ("
GPS navigation device ") in a marine application.
Global Positioning System
–
Automotive navigation system in a taxicab.
35.
Greenwich Sidereal Time
–
Sidereal time /saɪˈdɪəriəl/ is a time-keeping system that astronomers use to locate celestial objects. Using sidereal time it is possible to point a telescope to the proper coordinates in the night sky. Briefly, sidereal time is a scale that is based on Earths rate of rotation measured relative to the fixed stars rather than the Sun. From a given point, a star found at one location in the sky will be found at the same location on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun, just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earths rotation about its polar axis, a mean sidereal day is 23 hours,56 minutes,4.0916 seconds, the time it takes Earth to make one rotation relative to the vernal equinox. The longer true sidereal period is called a day by the International Earth Rotation. It is also referred to as the period of rotation. Maps of the stars in the night sky use declination and right ascension as coordinates and these correspond to latitude and longitude respectively. In the sky, the meridian is the north to south line that goes through the point directly overhead. Solar time is measured by the apparent diurnal motion of the Sun, a mean solar day is the average time between local solar noons. Earth makes one rotation around its axis in a sidereal day, so after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day, the stars are so far away that Earths movement along its orbit makes nearly no difference to their apparent direction, and so they return to their highest point in a sidereal day. Another way to see this difference is to notice that, relative to the stars, therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately 365. 24/366.24 times the length of the 24-hour solar day, Earths rotation is not a simple rotation around an axis that would always remain parallel to itself. Earths rotational axis itself rotates about an axis, orthogonal to Earths orbit. This phenomenon is called the precession of the equinoxes, because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation. In this reference frame, Earths rotation is close to constant and it is also in this reference frame that the tropical year, the year related to Earths seasons, represents one orbit of Earth around the Sun
Greenwich Sidereal Time
–
Key concepts
Greenwich Sidereal Time
–
Sidereal time vs solar time. Above left: a distant star (the small red circle) and the Sun are at
culmination, on the local meridian. Centre: only the distant star is at culmination (a mean
sidereal day). Right: a few minutes later the Sun is on the local meridian again. A
solar day is complete.
36.
Year
–
A year is the orbital period of the Earth moving in its orbit around the Sun. Due to the Earths axial tilt, the course of a year sees the passing of the seasons, marked by changes in weather, the hours of daylight, and, consequently, vegetation and soil fertility. In temperate and subpolar regions around the globe, four seasons are recognized, spring, summer, autumn. In tropical and subtropical regions several geographical sectors do not present defined seasons, but in the seasonal tropics, a calendar year is an approximation of the number of days of the Earths orbital period as counted in a given calendar. The Gregorian, or modern, calendar, presents its calendar year to be either a common year of 365 days or a year of 366 days, as do the Julian calendars. For the Gregorian calendar the average length of the year across the complete leap cycle of 400 years is 365.2425 days. The ISO standard ISO 80000-3, Annex C, supports the symbol a to represent a year of either 365 or 366 days, in English, the abbreviations y and yr are commonly used. In astronomy, the Julian year is a unit of time, it is defined as 365.25 days of exactly 86400 seconds, totalling exactly 31557600 seconds in the Julian astronomical year. The word year is used for periods loosely associated with, but not identical to, the calendar or astronomical year, such as the seasonal year, the fiscal year. Similarly, year can mean the period of any planet, for example. The term can also be used in reference to any long period or cycle, west Saxon ġēar, Anglian ġēr continues Proto-Germanic *jǣran. Cognates are German Jahr, Old High German jār, Old Norse ár and Gothic jer, all the descendants of the Proto-Indo-European noun *yeh₁rom year, season. Cognates also descended from the same Proto-Indo-European noun are Avestan yārǝ year, Greek ὥρα year, season, period of time, Old Church Slavonic jarŭ, Latin annus is from a PIE noun *h₂et-no-, which also yielded Gothic aþn year. Both *yeh₁-ro- and *h₂et-no- are based on verbal roots expressing movement, *h₁ey- and *h₂et- respectively, the Greek word for year, ἔτος, is cognate with Latin vetus old, from the PIE word *wetos- year, also preserved in this meaning in Sanskrit vat-sa- yearling and vat-sa-ras year. Derived from Latin annus are a number of English words, such as annual, annuity, anniversary, etc. per annum means each year, anno Domini means in the year of the Lord. No astronomical year has an number of days or lunar months. Financial and scientific calculations often use a 365-day calendar to simplify daily rates, in the Julian calendar, the average length of a year is 365.25 days. In a non-leap year, there are 365 days, in a year there are 366 days
Year
–
Key concepts
37.
Accuracy
–
Precision is a description of random errors, a measure of statistical variability. The two concepts are independent of other, so a particular set of data can be said to be either accurate, or precise. In the fields of science, engineering and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantitys true value. The precision of a measurement system, related to reproducibility and repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Although the two words precision and accuracy can be synonymous in colloquial use, they are contrasted in the context of the scientific method. A measurement system can be accurate but not precise, precise but not accurate, neither, for example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment, eliminating the systematic error improves accuracy but does not change precision. A measurement system is considered if it is both accurate and precise. Related terms include bias and error, the terminology is also applied to indirect measurements—that is, values obtained by a computational procedure from observed data. Statistical literature prefers to use the terms bias and variability instead of accuracy and precision, bias is the amount of inaccuracy and variability is the amount of imprecision. In military terms, accuracy refers primarily to the accuracy of fire, ideally a measurement device is both accurate and precise, with measurements all close to and tightly clustered around the true value. The accuracy and precision of a measurement process is established by repeatedly measuring some traceable reference standard. Such standards are defined in the International System of Units and maintained by national organizations such as the National Institute of Standards. This also applies when measurements are repeated and averaged, further, the central limit theorem shows that the probability distribution of the averaged measurements will be closer to a normal distribution than that of individual measurements. With regard to accuracy we can distinguish, the difference between the mean of the measurements and the value, the bias. Establishing and correcting for bias is necessary for calibration, the combined effect of that and precision. A common convention in science and engineering is to express accuracy and/or precision implicitly by means of significant figures, here, when not explicitly stated, the margin of error is understood to be one-half the value of the last significant place. For instance, a recording of 843.6 m, or 843.0 m, or 800.0 m would imply a margin of 0.05 m, while a recording of 8,436 m would imply a margin of error of 0.5 m
Accuracy
–
Accuracy is the proximity of measurement results to the true value; precision, the repeatability, or reproducibility of the measurement
38.
DUT1
–
The time correction DUT1 is the difference between Universal Time, which is defined by Earths rotation, and Coordinated Universal Time, which is defined by a network of precision atomic clocks. DUT1 = UT1 − UTC UTC is maintained via leap seconds, forecast values of DUT1 are published by IERS Bulletin A. Weekly updated values of DUT1 with 0.1 s precision are broadcast by several time signal services, including WWV and these services transmit one pulse per second of some sort. To represent positive DUT1 values from +0.1 to +0.8 seconds, the number of emphasized pulses gives the value of DUT1. Negative DUT1 values, from −0.1 to −0.8 seconds, are represented by emphasizing pulses 9 through 16. For example, a DUT1 value of −0.4 would be transmitted by emphasizing pulses 9 through 12, the Russian time signal RWM transmits an additional correction dUT1 in 0.02 s increments. Positive values of dUT1 from +0.02 to +0.08 s are encoded by emphasizing pulses 21 through 24, the actual value of DUT1 is approximated by the sum of the transmitted DUT1 + dUT1. The longwave RBU time signal also transmits dUT1, iTU-R Recommendation TF. 460-4, Standard-frequency and time-signal emissions. IERS Rapid Service/Prediction Center http, //scienceworld. wolfram. com/astronomy/Time. html http, //maia. usno. navy. mil/ser7/deltat. data
DUT1
–
Graph showing the difference in seconds between
UT1 and
UTC over time. A vertical transition indicates the use of a
leap second. The red portion of the graph indicates predicted values.
39.
Chatham Islands
–
The Chatham Islands form an archipelago in the Pacific Ocean about 650 kilometres east of mainland New Zealand. It consists of ten islands within a 40-kilometre radius, the largest of which are Chatham Island. The archipelago is called Rēkohu in the indigenous Moriori language, Moriori are the indigenous people of the Chatham Islands, and members of the Māori Ngāti Mutunga tribe have also settled on the island. It has officially been part of New Zealand since 1842 and includes the countrys easternmost point, the islands are at about 43°53′S 176°31′W, roughly 840 kilometres east of Christchurch, New Zealand. The nearest mainland New Zealand point to the Chatham Islands is Cape Turnagain, in the North Island at a distance of 650 kilometres, the nearest mainland city to the islands is Hastings, New Zealand, located 697 kilometres to the North-West. The two largest islands, Chatham Island and Pitt Island, constitute most of the area of 966 square kilometres. The islands sit on the Chatham Rise, a large, relatively shallowly submerged part of the Zealandia continent that stretches east from near the South Island. The Chatham Islands, which emerged only within the last four years, are the only part of the Chatham Rise showing above sea level. The islands are hilly with coasts being a mixture including cliffs and dunes, beaches. Chatham has a number of streams, including Te Awainanga and Tuku, Chatham and Pitt are the only inhabited islands, with the remaining smaller islands being conservation reserves with restricted or prohibited access. The livelihoods of the inhabitants depend on agriculture, with the island being an exporter of coldwater crayfish, the names of the main islands, in the order of occupation are, Chatham Islands have a maritime climate characterised by a narrow temperature range and relatively frequent rainfall. Its isolated position far from any sizeable landmass renders the record temperature for main settlement Waitangi to be just 23.8 °C. The climate is cool, wet and windy, with high temperatures between 15 and 20 °C in summer, and between 5 and 10 °C in July, the Southern Hemisphere winter. Snow is extremely rare, having being recorded near sea level in July 2015 after several decades, the International Date Line lies to the east of the Chathams, even though the islands lie east of 180° longitude. Of interest are the trees, with branches trailing almost horizontally in the lee of the wind. The ferns in the forest understory include Blechnum discolor, the islands are a breeding ground for huge flocks of seabirds and are home to a number of endemic birds, some of which are seabirds and others which live on the islands. The best known species are the magenta petrel and the black robin, Other endemic species are the Chatham oystercatcher, the Chatham gerygone, Chatham pigeon, Forbes parakeet, the Chatham snipe and the shore plover. The endemic Chatham shag, Pitt shag and the Chatham albatross are at risk of capture by a variety of fishing gear, including fishing lines, trawls, gillnets, for accounts and notes on seabird species seen in the Chathams between 1960 and 1993 online
Chatham Islands
–
The Chatham Islands from space.
Chatham Island is the largest,
Pitt Island is the second largest, and
South East Island is the small island to the right of Pitt.
Chatham Islands
–
Topographical map of the Chatham Islands
Chatham Islands
–
Massive
phytoplankton bloom around the islands.
Chatham Islands
–
Chatham Islands Forget-me-not (
Myosotidium hortensia)
40.
Timekeeping on Mars
–
Various schemes have been used or proposed for timekeeping on the planet Mars independently of Earth time and calendars. Mars has a tilt and a rotation period similar to those of Earth. Thus it experiences seasons of spring, summer, autumn and winter much like Earth, the average length of a Martian sidereal day is 24h 37m 22. 663s, and the length of its solar day is 24h 39m 35. 244147s. The corresponding values for Earth are 23h 56m 4. 0916s and 24h 00m 00. 002s and this yields a conversion factor of 1.02749125170 days/sol. Thus Mars solar day is only about 2. 7% longer than Earths and this results in the crews schedule sliding approximately 40 minutes later in Earth time each day. Wristwatches calibrated in Martian time, rather than Earth time, were used by many of the MER team members, Local solar time has a significant impact on planning the daily activities of Mars landers. Daylight is needed for the panels of landed spacecraft. Its temperature rises and falls rapidly at sunrise and sunset because Mars does not have the Earths thick atmosphere, alternative clocks for Mars have been proposed, but no mission has chosen to use such. These include a metric time schema, with millidays and centidays, as on Earth, on Mars there is also an equation of time that represents the difference between sundial time and uniform time. The equation of time is illustrated by an analemma, because of orbital eccentricity, the length of the solar day is not quite constant. Mars has a meridian, defined as passing through the small crater Airy-0. However, Mars does not have time zones defined at regular intervals from the prime meridian, each lander so far has used an approximation of local solar time as its frame of reference, as cities did on Earth before the introduction of standard time in the 19th century. Note that the standard for measuring longitude on Mars is planetocentric longitude. The older planetographic longitude was measured from 0°–360° West and used coordinates mapped onto the surface, MTC is a proposed Mars analog to Universal Time on Earth. It is defined as the solar time at Marss prime meridian. The definition of the Martian prime meridian has since been refined on the basis of spacecraft imagery as the center of the crater Airy-0 in Terra Meridiani, MTC is more closely analogous to UT1. Use of the term MTC as the name of a standard time for Mars first appeared in the Mars24 sunclock coded by the NASA Goddard Institute for Space Studies. It replaced Mars24s previous use of the term Airy Mean Time, in an astronomical context, GMT is a deprecated name for Universal Time, or sometimes more specifically for UT1
Timekeeping on Mars
–
On Earth
Timekeeping on Mars
–
Martian season lengths and time as compared to
seasons on the Earth.
41.
Unix time
–
It is used widely in Unix-like and many other operating systems and file formats. Because it does not handle leap seconds, it is neither a linear representation of time nor a true representation of UTC, Unix time may be checked on most Unix systems by typing date +%s on the command line. The 32-bit representation of Unix time will end after the completion of 2,147,483, 647( seconds from the beginning and this is referred to as the Year 2038 problem where the 32-bit Unix time will overflow and will take the actual count to negative. Two layers of encoding make up Unix time, the first layer encodes a point in time as a scalar real number which represents the number of seconds that have passed since the beginning of 00,00,00 UTC Thursday 1, January 1970. The second layer encodes that number as a sequence of bits or decimal digits, as is standard with UTC, this article labels days using the Gregorian calendar, and counts times within each day in hours, minutes, and seconds. Modern Unix time is based on UTC, which counts time using SI seconds, and breaks up the span of time into days almost always 86,400 seconds long and this extra second keeps the days synchronized with the rotation of the Earth, per Universal Time. The Unix epoch is the time 00,00,00 UTC on 1 January 1970, there is a problem with this definition, in that UTC did not exist in its current form until 1972, this issue is discussed below. For brevity, the remainder of this section uses ISO8601 date format, in which the Unix epoch is 1970-01-01T00,00, the Unix time number is zero at the Unix epoch, and increases by exactly 86,400 per day since the epoch. Thus 2004-09-16T00,00, 00Z,12,677 days after the epoch, is represented by the Unix time number 12,677 ×86,400 =1095292800. This can be extended backwards from the epoch too, using numbers, thus 1957-10-04T00,00. Within each day, the Unix time number is calculated as in the preceding paragraph at midnight UTC, and increases by exactly 1 per second since midnight. Thus 2004-09-16T17,55,43. 54Z,64,543.54 s since midnight on the day in the example above, is represented by the Unix time number 1095292800 +64543.54 =1095357343.54. On dates before the epoch the number increases, thus becoming less negative. Because Unix time is based on the Unix epoch, it is referred to as epoch time. The above scheme means that on a normal UTC day, which has a duration of 86,400 seconds, the Unix time number increases by exactly 86,400 each day, regardless of how long the day is. When a leap second is deleted, the Unix time number jumps up by 1 where the second was deleted. For example, this is what happened on strictly conforming POSIX.1 systems at the end of 1998, Observe that when a positive leap second occurs the Unix time numbers repeat themselves. The Unix time number 915148800.50 is ambiguous, it can refer either to the instant in the middle of the second, or to the instant one second later
Unix time
–
Unix time passed 1,000,000,000 seconds in 2001-09-09T01:46:40Z. It was celebrated in Copenhagen, Denmark at a party held by
DKUUG (at 03:46:40 local time).
42.
UTC
–
Coordinated Universal Time, abbreviated to UTC, is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean time at 0° longitude. It is one of closely related successors to Greenwich Mean Time. For most purposes, UTC is considered interchangeable with GMT, the first Coordinated Universal Time was informally adopted on 1 January 1960. This change also adopted leap seconds to simplify future adjustments, a number of proposals have been made to replace UTC with a new system that would eliminate leap seconds, but no consensus has yet been reached. Leap seconds are inserted as necessary to keep UTC within 0.9 seconds of universal time, see the Current number of leap seconds section for the number of leap seconds inserted to date. The official abbreviation for Coordinated Universal Time is UTC and this abbreviation arose from a desire by the International Telecommunication Union and the International Astronomical Union to use the same abbreviation in all languages. English speakers originally proposed CUT, while French speakers proposed TUC, the compromise that emerged was UTC, which conforms to the pattern for the abbreviations of the variants of Universal Time. Time zones around the world are expressed using positive or negative offsets from UTC, the westernmost time zone uses UTC−12, being twelve hours behind UTC, the easternmost time zone, theoretically, uses UTC+12, being twelve hours ahead of UTC. In 1995, the nation of Kiribati moved those of its atolls in the Line Islands from UTC-10 to UTC+14 so that the country would all be on the same day. UTC is used in internet and World Wide Web standards. The Network Time Protocol, designed to synchronise the clocks of computers over the internet, computer servers, online services and other entities that rely on having a universally accepted time use UTC as it is more specific than GMT. If only limited precision is needed, clients can obtain the current UTC from a number of official internet UTC servers, for sub-microsecond precision, clients can obtain the time from satellite signals. UTC is also the standard used in aviation, e. g. for flight plans. Weather forecasts and maps all use UTC to avoid confusion about time zones, the International Space Station also uses UTC as a time standard. Amateur radio operators often schedule their radio contacts in UTC, because transmissions on some frequencies can be picked up by many time zones, UTC is also used in digital tachographs used on large goods vehicles under EU and AETR rules. UTC divides time into days, hours, minutes and seconds, days are conventionally identified using the Gregorian calendar, but Julian day numbers can also be used. Each day contains 24 hours and each hour contains 60 minutes, the number of seconds in a minute is usually 60, but with an occasional leap second, it may be 61 or 59 instead
UTC
UTC
43.
Jet Propulsion Laboratory
–
The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address
Jet Propulsion Laboratory
–
Aerial view of JPL in Pasadena, California
Jet Propulsion Laboratory
–
The control room at JPL
Jet Propulsion Laboratory
–
MSL mockup compared with the
Mars Exploration Rover and
Sojourner rover by the Jet Propulsion Laboratory on May 12, 2008
Jet Propulsion Laboratory
–
Research rockets on display at JPL.
44.
Standard Time Act
–
The Standard Time Act of 1918, also known as the Calder Act, was the first United States federal law implementing Standard time and Daylight saving time in the United States. It authorized the Interstate Commerce Commission to define each time zone, the section concerning daylight saving time was repealed by the act titled An Act For the repeal of the daylight-saving law, Pub. L. 280, enacted August 20,1919, over President Woodrow Wilsons veto, section 264 of the act mistakenly placed most of the state of Idaho in UTC−06,00 CST Central Standard Time, but was amended in 2007 by Congress to UTC−07,00 MST Mountain Standard Time. MST was observed prior to the correction
Standard Time Act
–
Standard Time Act
45.
Peter Galison
–
Peter Louis Galison is the Joseph Pellegrino University Professor in history of science and physics at Harvard University. He received his Ph. D. at Harvard University in both physics and in the history of science in 1983 and his publications include Image and Logic, A Material Culture of Microphysics and Einsteins Clocks, Poincarés Maps, Empires of Time. His most recent book, co-authored with Lorraine Daston, is titled Objectivity, before moving to Harvard, Galison taught for several years at Stanford University, where he was professor of history, philosophy, and physics. He is considered part of the Stanford School of philosophy of science along with Ian Hacking, John Dupré, and Nancy Cartwright. Galison developed a film for the History Channel on the development of the hydrogen bomb and he is on the editorial board of Critical Inquiry and was a MacArthur Fellow in 1996. Galison has been involved in the production of three documentary films, the second, Secrecy, which Galison directed with Harvard filmmaker Robb Moss, is about the costs and benefits of government secrecy, and premiered at the 2008 Sundance Film Festival. Also from Harvard, Ruth Lingford worked on the animation for Secrecy, Galison completed his third documentary film Containment, also directed with Robb Moss, in 2015. It premiered at the 2015 Full Frame Documentary Film Festival, and has shown at film festivals around the world including in Brazil, Switzerland. Chicago, Illinois, University of Chicago Press, big science, the growth of large-scale research. The disunity of science, boundaries, contexts, and power, Image and logic, a material culture of microphysics. Chicago, Illinois, University of Chicago Press, Einsteins clocks and Poincarés maps, empires of time. New York, New York, W. W. Norton, New York Cambridge, Massachusetts, Zone Books Distributed by the MIT Press. Galison, Peter, Holton, Gerald, Schweber, Silvan S. Einstein for the 21st century, his legacy in science, art, Princeton, New Jersey, Princeton University Press. The Ultimate Weapon, The H-Bomb Dilemma Writer/producer,44 minutes, premiere, Full Frame Documentary Film Festival, Durham, North Carolina
Peter Galison
–
Peter Galison at the 2007
History of Science Society meeting
46.
International Standard Book Number
–
The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
International Standard Book Number
–
A 13-digit ISBN, 978-3-16-148410-0, as represented by an
EAN-13 bar code
47.
United States Naval Observatory
–
The USNO operates the Master Clock, which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, aside from its scientific mission, a house located within the Naval Observatory complex serves as the official residence of the Vice President of the United States. President John Quincy Adams, who in 1825 signed the bill for the creation of an observatory just before leaving presidential office, had intended for it to be called the National Observatory. The names National Observatory and Naval Observatory were both used for 10 years, until a ruling was passed to use the latter. Adams had made protracted efforts to bring astronomy to a level at that time. He spent many nights at the observatory, watching and charting the stars, established by the order of the United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments, the Observatory rose from humble beginnings. Placed under the command of Lieutenant Louis M. Goldsborough, with an budget of $330, its primary function was the restoration, repair. It was made into an observatory in 1842 via a federal law. Lieutenant James Melville Gilliss was put in charge of obtaining the instruments needed, lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and scientific devices and books. The observatorys primary mission was to care for the United States Navys marine chronometers, charts and it calibrated ships chronometers by timing the transit of stars across the meridian. These facilities were listed on the National Register of Historic Places in 2017, the first superintendent was Navy Commander Matthew Fontaine Maury. Maury had the worlds first vulcanized time ball, created to his specifications by Charles Goodyear for the U. S. Observatory and it was the first time ball in the United States, being placed into service in 1845, and the 12th in the world. Maury kept accurate time by the stars and planets, the time ball was dropped every day except Sunday precisely at the astronomically defined moment of Mean Solar Noon, enabling all ships and civilians to know the exact time. Time was also sold to the railroads and was used in conjunction with railroad chronometers to schedule American rail transport, early in the 20th century, the Arlington Time Signal broadcast this service to wireless receivers. In 1849 the Nautical Almanac Office was established in Cambridge, Massachusetts as a separate organization and it was moved to Washington, D. C. in 1866, colocating with the U. S. Naval Observatory in 1893. On September 20,1894, the NAO became a branch of USNO, the astronomical measurements taken of the transit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of the AU. Relying heavily on methods, the naval observers returned 350 photographic plates in 1874. This calculated distance was a significant improvement over several previous estimates, the telescope used for the discovery of the Moons of Mars was the 26-inch refractor, then located at Foggy Bottom
United States Naval Observatory
–
Aerial view of the U.S. Naval Observatory
United States Naval Observatory
–
The Seal of the USNO with a quote from the
Astronomicon, Adde gubernandi studium: Pervenit in astra, et pontum caelo conjunxit, "Increase the study of navigation: it arrives in the stars, and marries the sea with heaven"
United States Naval Observatory
–
Naval Observatory Flagstaff Station in Operation
United States Naval Observatory
–
Number One Observatory Circle, official home of the Vice President of the United States
48.
General Services Administration
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The General Services Administration is an independent agency of the United States government, established in 1949 to help manage and support the basic functioning of federal agencies. GSA employs about 12,000 federal workers and has an operating budget of roughly $26.3 billion. GSA oversees $66 billion of procurement annually and it contributes to the management of about $500 billion in U. S. federal property, divided chiefly among 8,300 owned and leased buildings and a 210,000 vehicle motor pool. GSAs business lines include the Federal Acquisition Service, the Public Buildings Service, the GSA is member of the Procurement G6, an informal group leading the use of framework agreements and e-procurement instruments in public procurement. In 1947 President Harry Truman asked former President Herbert Hoover to lead what became known as the Hoover Commission to make recommendations to reorganize the operations of the federal government, one of the recommendations of the commission was the establishment of an Office of the General Services. This proposed office would combine the responsibilities of the following organizations, General Jess Larson, Administrator of the War Assets Administration, was named GSAs first Administrator. The first job awaiting Administrator Larson and the newly formed GSA was a renovation of the White House. The structure had fallen into such a state of disrepair by 1949 that one inspector of the time said the structure was standing “purely from habit. Everything, except the four walls without a roof, was stripped down. GSA completed the renovation in 1952, GSA headquarters, located at Eighteenth and F Streets, NW, was U. S. General Services Administration Building listed on the National Register of Historic Places in 1986 as Interior Department Offices, in 1960, GSA created the Federal Telecommunications System, a government-wide intercity telephone system. In 1970, the Nixon administration created the Consumer Product Information Coordinating Center, the Federal Buildings Fund was initiated in 1974, which allowed the GSA to issue rent bills to federal agencies. In 1972, the GSA established the Automated Data and Telecommunications Service, in 1973, the GSA created the Office of Federal Management Policy. GSA’s Office of Acquisition Policy centralized procurement policy in 1978, in 1984, GSA introduced the federal government to the use of charge cards, known as the GMA SmartPay system. The National Archives and Records Administration was spun off into an independent agency in 1985, the same year, the GSA began to provide governmentwide policy oversight and guidance for federal real property management as a result of an Executive Order signed by President Ronald Reagan. In 2003, the Federal Protective Service was moved to the Department of Homeland Security, in 2005, GSA reorganized to merge the Federal Supply Service and Federal Technology Service business lines into the Federal Acquisition Service. On April 3,2009, President Barack Obama nominated Martha N. Johnson to serve as the GSA Administrator, after a 9-month delay, the United States Senate confirmed her nomination on February 4,2010. In July 1991, GSA contractors began the excavation of what is now the Ted Weiss Federal Building in New York City, when initial excavation disturbed burials, destroying skeletons and artifacts, GSA sent archaeologists to excavate—but hid their findings from the public
General Services Administration
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Thoughtful analysis to balance GSA preservation, cost, and performance goals supported historic window retention with replacement of non-historic windows at this 1930 courthouse
General Services Administration
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Official seal
49.
Time
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Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future. Time is often referred to as the dimension, along with the three spatial dimensions. Time has long been an important subject of study in religion, philosophy, and science, nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems. Two contrasting viewpoints on time divide prominent philosophers, one view is that time is part of the fundamental structure of the universe—a dimension independent of events, in which events occur in sequence. Isaac Newton subscribed to this realist view, and hence it is referred to as Newtonian time. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that time is neither an event nor a thing, Time in physics is unambiguously operationally defined as what a clock reads. Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities, Time is used to define other quantities—such as velocity—so defining time in terms of such quantities would result in circularity of definition. The operational definition leaves aside the question there is something called time, apart from the counting activity just mentioned, that flows. Investigations of a single continuum called spacetime bring questions about space into questions about time, questions that have their roots in the works of early students of natural philosophy. Furthermore, it may be there is a subjective component to time. Temporal measurement has occupied scientists and technologists, and was a motivation in navigation. Periodic events and periodic motion have long served as standards for units of time, examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the unit of time, the second, is defined by measuring the electronic transition frequency of caesium atoms. Time is also of significant social importance, having economic value as well as value, due to an awareness of the limited time in each day. In day-to-day life, the clock is consulted for periods less than a day whereas the calendar is consulted for periods longer than a day, increasingly, personal electronic devices display both calendars and clocks simultaneously. The number that marks the occurrence of an event as to hour or date is obtained by counting from a fiducial epoch—a central reference point. Artifacts from the Paleolithic suggest that the moon was used to time as early as 6,000 years ago. Lunar calendars were among the first to appear, either 12 or 13 lunar months, without intercalation to add days or months to some years, seasons quickly drift in a calendar based solely on twelve lunar months
Time
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The flow of
sand in an
hourglass can be used to keep track of elapsed time. It also concretely represents the
present as being between the
past and the
future.
Time
Time
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Horizontal
sundial in
Taganrog
Time
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A contemporary
quartz watch
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".
