1.
Season
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A season is a division of the year marked by changes in weather, ecology and hours of daylight. Seasons result from the orbit of the Earth around the Sun. During May, June, and July, the northern hemisphere is exposed to direct sunlight because the hemisphere faces the sun. The same is true of the hemisphere in November, December. It is the tilt of the Earth that causes the Sun to be higher in the sky during the months which increases the solar flux. However, due to lag, June, July, and August are the hottest months in the northern hemisphere and December, January. In temperate and subpolar regions, four calendar-based seasons are recognized, spring, summer, autumn or fall. Ecologists often use a model for temperate climate regions, prevernal, vernal, estival, serotinal, autumnal. Many tropical regions have two seasons, the rainy, wet, or monsoon season and the dry season, some have a third cool, mild, or harmattan season. Seasons often held special significance for agrarian societies, whose lives revolved around planting and harvest times, in some parts of the world, some other seasons capture the timing of important ecological events such as hurricane season, tornado season, and wildfire season. The most historically important of these are the three seasons—flood, growth, and low water—which were previously defined by the annual flooding of the Nile in Egypt. The seasons result from the Earths axis of rotation being tilted with respect to its orbital plane by an angle of approximately 23.5 degrees, regardless of the time of year, the northern and southern hemispheres always experience opposite seasons. This is because during summer or winter, one part of the planet is directly exposed to the rays of the Sun than the other. For approximately half of the year, the northern hemisphere tips toward the Sun, for the other half of the year, the same happens, but in the southern hemisphere instead of the northern, with the maximum around December 21. The two instants when the Sun is directly overhead at the Equator are the equinoxes. Also at that moment, both the North Pole and the South Pole of the Earth are just on the terminator, and hence day and night are equally divided between the northern and southern hemispheres. Around the March equinox, the northern hemisphere will be experiencing spring as the hours of daylight increase, the effect of axial tilt is observable as the change in day length and altitude of the Sun at noon during a year. Between this effect and the daylight hours, the axial tilt of the Earth accounts for most of the seasonal variation in climate in both hemispheres
2.
Mars
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Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
3.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
4.
Axial tilt
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In astronomy, axial tilt, also known as obliquity, is the angle between an objects rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. At an obliquity of zero, the two axes point in the direction, i. e. the rotational axis is perpendicular to the orbital plane. Over the course of an orbit, the obliquity usually does not change considerably, and this causes one pole to be directed more toward the Sun on one side of the orbit, and the other pole on the other side — the cause of the seasons on the Earth. Earths obliquity oscillates between 22.1 and 24.5 degrees on a 41, 000-year cycle, the mean obliquity is currently 23°26′13. 4″. There are two methods of specifying tilt. The IAU also uses the rule to define a positive pole for the purpose of determining orientation. Using this convention, Venus is tilted 177° and it is denoted by the Greek letter ε. Earth currently has a tilt of about 23. 4°. This value remains about the relative to a stationary orbital plane throughout the cycles of axial precession. But the ecliptic due to planetary perturbations, and the obliquity of the ecliptic is not a fixed quantity. At present, it is decreasing at a rate of about 47″ per century, Earths obliquity may have been reasonably accurately measured as early as 1100 BC in India and China. The ancient Greeks had good measurements of the obliquity since about 350 BC, about 830 AD, the Caliph Al-Mamun of Baghdad directed his astronomers to measure the obliquity, and the result was used in the Arab world for many years. It was widely believed, during the Middle Ages, that both precession and Earths obliquity oscillated around a value, with a period of 672 years. Earths axis remains tilted in the direction with reference to the background stars throughout a year. This means that one pole will be directed away from the Sun at one side of the orbit and this is the cause of Earths seasons. Summer occurs in the Northern hemisphere when the pole is directed toward the Sun. Variations in Earths axial tilt can influence the seasons and is likely a factor in climate change. The exact angular value of the obliquity is found by observation of the motions of Earth, from 1984, the Jet Propulsion Laboratorys DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac
5.
Spring (season)
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Spring is one of the four conventional temperate seasons, following winter and preceding summer. There are various definitions of spring, but local usage of the term varies according to local climate, cultures. When it is spring in the Northern Hemisphere, it will be autumn in the Southern Hemisphere, at the spring equinox, days are approximately 12 hours long with day length increasing as the season progresses. Spring and springtime refer to the season, and also to ideas of rebirth, rejuvenation, renewal, resurrection, subtropical and tropical areas have climates better described in terms of other seasons, e. g. dry or wet, monsoonal or cyclonic. Often, cultures have locally defined names for seasons which have little equivalence to the terms originating in Europe, Spring is the time when many plants begin to grow and flower. Meteorologists generally define four seasons in many areas, spring, summer, autumn. These are demarcated by the values of their average temperatures on a monthly basis, the three warmest months are by definition summer, the three coldest months are winter and the intervening gaps are spring and autumn. Spring, when defined in this manner, can start on different dates in different regions, in most Northern Hemisphere, temperate locations, spring months are March, April and May, although differences exist from country to country. Most Southern Hemisphere, temperate locations have opposing seasons with spring in September, October and November, in Australia and New Zealand, spring conventionally begins on 1 September and ends 30 November. In some cultures in the Northern Hemisphere, the astronomical Vernal equinox is taken to mark the first day of spring, in Persian culture the first day of spring is the first day of the first month which begins on 20 or 21 March. In other traditions, the equinox is taken as mid-spring, similarly, according to the Celtic tradition, which is based solely on daylight and the strength of the noon sun, spring begins in early February and continues until early May. In Ireland, spring traditionally starts on February 1, St Brigids Day, the beginning of spring is not always determined by fixed calendar dates. These indicators, along with the beginning of spring, vary according to the local climate, most ecologists divide the year into six seasons that have no fixed dates. In addition to spring, ecological reckoning identifies an earlier separate prevernal season between the hibernal and vernal seasons and this is a time when only the hardiest flowers like the crocus are in bloom, sometimes while there is still some snowcover on the ground. During early spring, the axis of the Earth is increasing its tilt relative to the Sun, the hemisphere begins to warm significantly, causing new plant growth to spring forth, giving the season its name. Any snow begins to melt, swelling streams with runoff and any frosts become less severe, in climates that have no snow, and rare frosts, air and ground temperatures increase more rapidly. Many flowering plants bloom at this time of year, in a succession, sometimes beginning when snow is still on the ground. In normally snowless areas, spring may begin as early as February, heralded by the blooming of deciduous magnolias, cherries, and quince, or August in the same way
6.
Summer
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Summer is the hottest of the four temperate seasons, falling between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, the date of the beginning of summer varies according to climate, tradition and culture. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, a variable seasonal lag means that the meteorological center of the season, which is based on average temperature patterns, occurs several weeks after the time of maximal insolation. Under meteorological definitions, all seasons are set to start at the beginning of a calendar month. This meteorological definition of summer also aligns with the commonly viewed notion of summer as the season with the longest days of the year, the meteorological reckoning of seasons is used in Australia, Austria, Denmark, the former Soviet Union and Japan. It is also used by many in the United Kingdom, in Ireland, the summer months according to the national meteorological service, Met Éireann, are June, July and August. However, according to the Irish Calendar, summer begins on 1 May, school textbooks in Ireland follow the cultural norm of summer commencing on 1 May rather than the meteorological definition of 1 June. Reckoning by hours of daylight alone, summer solstice marks the midpoint, not the beginning, midsummer takes place over the shortest night of the year, which is the summer solstice, or on a nearby date that varies with tradition. Where a seasonal lag of half a season or more is common, by this method, in North America, summer is the period from the summer solstice to the autumn equinox. The similar Canadian tradition starts summer on Victoria Day one week prior and ends, as in the United States, on Labour Day. In Chinese astronomy, summer starts on or around 5 May, with the known as lìxià, i. e. establishment of summer. In Australia and New Zealand, summer begins on 1 December. Summer is traditionally associated with hot or warm weather, in the Mediterranean regions, it is also associated with dry weather, while in other places it is associated with rainy weather. The wet season is the period of vegetation growth within the savanna climate regime. Where the wet season is associated with a shift in the prevailing winds. In the northern Atlantic Ocean, a tropical cyclone season occurs from 1 June to 30 November. The statistical peak of the Atlantic hurricane season is 10 September, the Northeast Pacific Ocean has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March, in the North Indian basin, storms are most common from April to December, with peaks in May and November
7.
Autumn
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Autumn, also known as fall in North American English, is one of the four temperate seasons. One of its features is the shedding of leaves from deciduous trees. Some cultures regard the autumnal equinox as mid-autumn, while others with a longer temperature lag treat it as the start of autumn. Meteorologists use a definition based on months, with autumn being September, October and November in the northern hemisphere, in North America, autumn is usually considered to start with the September equinox and end with the winter solstice. As daytime and nighttime temperatures decrease, trees shed their leaves, in traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the meteorological service. In Australia and New Zealand, autumn officially begins on 1 March, the word autumn comes from the ancient Etruscan root autu- and has within it connotations of the passing of the year. It was borrowed by the neighbouring Romans, and became the Latin word autumnus, after the Roman era, the word continued to be used as the Old French word autompne or autumpne in Middle English, and was later normalized to the original Latin. In the Medieval period, there are examples of its use as early as the 12th century. Before the 16th century, harvest was the usually used to refer to the season. The alternative word fall for the season traces its origins to old Germanic languages, the exact derivation is unclear, with the Old English fiæll or feallan and the Old Norse fall all being possible candidates. However, these all have the meaning to fall from a height and are clearly derived either from a common root or from each other. The term came to denote the season in 16th century England, during the 17th century, English emigration to the British colonies in North America was at its peak, and the new settlers took the English language with them. While the term gradually became obsolete in Britain, it became the more common term in North America. The name backend, a common name for the season in Northern England, has today been largely replaced by the name autumn. Association with the transition from warm to cold weather, and its status as the season of the primary harvest, has dominated its themes. In Western cultures, personifications of autumn are usually pretty, well-fed females adorned with fruits, vegetables, many cultures feature autumnal harvest festivals, often the most important on their calendars. There are also the many North American Indian festivals tied to harvest of ripe foods gathered in the wild, the Chinese Mid-Autumn or Moon festival, and many others
8.
Winter
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Winter is the coldest season of the year in polar and temperate climates, between autumn and spring. Winter is caused by the axis of the Earth in that hemisphere being oriented away from the Sun, different cultures define different dates as the start of winter, and some use a definition based on weather. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, in many regions, winter is associated with snow and freezing temperatures. The moment of winter solstice is when the elevation with respect to the North or South Pole is at its most negative value, meaning this day will have the shortest day. The English word winter comes from the Proto-Indo-European root wend, relating to water, the tilt of the Earths axis relative to its orbital plane plays a large role in the formation of weather. The Earth is tilted at an angle of 23. 44° to the plane of its orbit, when it is winter in the Northern Hemisphere, the Southern Hemisphere faces the Sun more directly and thus experiences warmer temperatures than the Northern Hemisphere. Conversely, winter in the Southern Hemisphere occurs when the Northern Hemisphere is tilted more toward the Sun, from the perspective of an observer on the Earth, the winter Sun has a lower maximum altitude in the sky than the summer Sun. During winter in either hemisphere, the altitude of the Sun causes the sunlight to hit that hemisphere at an oblique angle. In regions experiencing winter, the amount of solar radiation is spread out over a larger area. This effect is compounded by the distance that the light must travel through the atmosphere. Compared with these effects, the changes in the distance of the earth from the sun are negligible, the manifestation of the meteorological winter in the northerly snow–prone parallels is highly variable depending on elevation, position versus marine winds and the amount of precipitation. A case in point is Canada, a country associated with tough winters. Winnipeg on the Great Plains at a distance from large bodies of water has a January high of −11.3 °C. In comparison, Vancouver on the coast with an influence from moderating Pacific winds has a January low of 1.4 °C with days well above freezing at 6.9 °C. Both areas are on the 49th parallel north and in the western half of the continent. Winter is often defined by meteorologists to be the three months with the lowest average temperatures. This corresponds to the months of December, January and February in the Northern Hemisphere, the coldest average temperatures of the season are typically experienced in January or February in the Northern Hemisphere and in June, July or August in the Southern Hemisphere. Blizzards often develop and cause many transportation delays, diamond dust, also known as ice needles or ice crystals, forms at temperatures approaching −40 °F due to air with slightly higher moisture from aloft mixing with colder, surface based air
9.
Orbital eccentricity
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The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is an orbit, values between 0 and 1 form an elliptical orbit,1 is a parabolic escape orbit. The term derives its name from the parameters of conic sections and it is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit, the eccentricity of this Kepler orbit is a non-negative number that defines its shape. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola, radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits have zero angular momentum and hence eccentricity equal to one, keeping the energy constant and reducing the angular momentum, elliptic, parabolic, and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity. From Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros out of the center, from ἐκ- ek-, eccentric first appeared in English in 1551, with the definition a circle in which the earth, sun. Five years later, in 1556, a form of the word was added. The eccentricity of an orbit can be calculated from the state vectors as the magnitude of the eccentricity vector, e = | e | where. For elliptical orbits it can also be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p =1 −2 r a r p +1 where, rp is the radius at periapsis. For Earths annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈1.034 relative to center point of path, the eccentricity of the Earths orbit is currently about 0.0167, the Earths orbit is nearly circular. Venus and Neptune have even lower eccentricity, over hundreds of thousands of years, the eccentricity of the Earths orbit varies from nearly 0.0034 to almost 0.058 as a result of gravitational attractions among the planets. The table lists the values for all planets and dwarf planets, Mercury has the greatest orbital eccentricity of any planet in the Solar System. Such eccentricity is sufficient for Mercury to receive twice as much solar irradiation at perihelion compared to aphelion, before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit
10.
Sundial
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A sundial is a device that tells the time of day by the apparent position of the Sun in the sky. In the narrowest sense of the word it consists of a flat plate, as the sun appears to move across the sky, the shadow aligns with different hour-lines which are marked on the dial to indicate the time of day. The style is the edge of the gnomon, though a single point or nodus may be used. The gnomon casts a shadow, the shadow of the style shows the time. The gnomon may be a rod, a wire or a decorated metal casting. The style must be parallel to the axis of the Earths rotation for the sundial to be throughout the year. The styles angle from horizontal is equal to the geographical latitude. In a broader sense a sundial is any device that uses the suns altitude or azimuth to show the time, in addition to their time-telling function, sundials are valued as decorative objects, as literary metaphors and as objects of mathematical study. It is common for inexpensive mass-produced decorative sundials to have incorrectly aligned gnomons and hour-lines, there are several different types of sundials. Some sundials use a shadow or the edge of a shadow while others use a line or spot of light to indicate the time, the shadow-casting object, known as a gnomon, may be a long thin rod or other object with a sharp tip or a straight edge. Sundials employ many types of gnomon, the gnomon may be fixed or moved according to the season. It may be oriented vertically, horizontally, aligned with the Earths axis, given that sundials use light to indicate time, a line of light may be formed by allowing the suns rays through a thin slit or focusing them through a cylindrical lens. A spot of light may be formed by allowing the suns rays to pass through a hole or by reflecting them from a small circular mirror. Sundials also may use many types of surfaces to receive the light or shadow, planes are the most common surface, but partial spheres, cylinders, cones and other shapes have been used for greater accuracy or beauty. Sundials differ in their portability and their need for orientation, the installation of many dials requires knowing the local latitude, the precise vertical direction, and the direction to true North. Portable dials are self-aligning, for example, it may have two dials that operate on different principles, such as a horizontal and analemmatic dial, mounted together on one plate, in these designs, their times agree only when the plate is aligned properly. Sundials indicate the solar time, unless corrected for some other time. To obtain the clock time, three types of corrections need to be made
11.
Sidereal day
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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
12.
International System of Units
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The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
13.
Solar day
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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
14.
Sidereal time
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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
15.
Mars Pathfinder
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Mars Pathfinder is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight wheeled robotic Mars rover named Sojourner, the lander then opened, exposing the rover which conducted many experiments on the Martian surface. The mission carried a series of instruments to analyze the Martian atmosphere, climate, geology. The mission was directed by the Jet Propulsion Laboratory, a division of the California Institute of Technology, the project manager was JPLs Tony Spear. This mission was the first of a series of missions to Mars that included rovers, although the Soviet Union successfully sent rovers to the Moon as part of the Lunokhod program in the 1970s, its attempts to use rovers in its Mars program failed. The Mars Pathfinder was also remarkable for its low cost relative to other unmanned space missions to Mars. Originally, the mission was conceived as the first of the Mars Environmental Survey program, to prove that the development of faster, better and cheaper spacecraft was possible. To show that it was possible to send a load of scientific instruments to another planet with a simple system, to demonstrate NASAs commitment to low-cost planetary exploration by finishing the mission with a total expenditure of $280 million, including the launch vehicle and mission operations. The Mars Pathfinder conducted different investigations on the Martian soil using three scientific instruments, the MET structure included three windsocks mounted at three heights on a pole, the topmost at about one meter and generally registered winds from the West. The Sojourner rover had an Alpha Proton X-ray Spectrometer, which was used to analyze the components of the rocks, the rover also had two black-and-white cameras and a color one. A third camera with the resolution but taking color images was located on the back, near the APXS. It provided images of the APXSs target area and the tracks on the ground. All three cameras were CCDs manufactured by Eastman Kodak Company, and were controlled by the rovers CPU and they all had auto-exposure and capabilities for handling bad pixels, and the image parameters were included in the transmitted images as part of the image header. The rover could compress the front cameras images using the block truncation coding algorithm, the cameras optical resolution was sufficient to resolve 0.6 cm details across a 0.65 m range. Scientists chose it because they found it to be a relatively safe surface to land on and one that contained a wide variety of rocks deposited during a catastrophic flood. After the landing, at 19. 13°N33. 22°W /19.13, -33.22, succeeded, the landers on-board computer used redundant on-board accelerometers to determine the timing of the parachute inflation. Twenty seconds later the heatshield was pyrotechnically released, another twenty seconds later the lander was separated and lowered from the backshell on a 20 m bridle. When the lander reached 1.6 km above the surface and this information was used by the computer to determine the precise timing of the landing events that followed
16.
Mars Exploration Rover
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NASAs Mars Exploration Rover mission is an ongoing robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars. It began in 2003 with the sending of the two rovers, MER-A Spirit and MER-B Opportunity—to explore the Martian surface and geology, both rovers outlived their planned missions of 90 Martian solar days by far. MER-A Spirit was active until 2010, the success of the two MERs led to another mission, sending a bigger rover Curiosity in 2012. The missions scientific objective was to search for and characterize a wide range of rocks, the mission is part of NASAs Mars Exploration Program, which includes three previous successful landers, the two Viking program landers in 1976 and Mars Pathfinder probe in 1997. The total cost of building, launching, landing and operating the rovers on the surface for the initial 90-sol primary mission was US$820 million, since the rovers have continued to function beyond their initial 90 sol primary mission, they have each received five mission extensions. The fifth mission extension was granted in October 2007, and ran to the end of 2009, the total cost of the first four mission extensions was $104 million, and the fifth mission extension is expected to cost at least $20 million. However, the dust storms lifted, allowing them to resume operations, on May 1,2009, during its fifth mission extension, Spirit became stuck in soft soil on Mars. This mode would enable Spirit to assist scientists in ways that a mobile platform could not, in recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honor,37452 Spirit and 39382 Opportunity. The mission is managed for NASA by the Jet Propulsion Laboratory, which designed, built, the search for evidence of habitability, taphonomy, and organic carbon on the planet Mars is now a primary NASA objective. The scientific objectives of the Mars Exploration Rover mission are to, Search for and characterize a variety of rocks, in particular, samples sought include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity. Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites, determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, perform calibration and validation of surface observations made by Mars Reconnaissance Orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit, Search for iron-containing minerals, and to identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates. Characterize the mineralogy and textures of rocks and soils to determine the processes that created them, Search for geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life, the MER-A and MER-B probes were launched on June 10,2003 and July 7,2003, respectively. The launch vehicles were integrated onto pads right next to other, with MER-A on CCAFS SLC-17A. The dual pads allowed for working the 15- and 21-day planetary launch periods close together, the last possible day for MER-A was June 19,2003. NASAs Launch Services Program managed the launch of both spacecraft, the probes landed in January 2004 in widely separated equatorial locations on Mars
17.
Phoenix (spacecraft)
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Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25,2008, Mission scientists used instruments aboard the lander to search for environments suitable for microbial life on Mars, and to research the history of water there. The total mission cost was about US $386 million, which includes cost of the launch, the multi-agency program was headed by the Lunar and Planetary Laboratory at the University of Arizona, under the direction of NASAs Jet Propulsion Laboratory. It was the first mission to Mars led by a university in NASA history. The operational funding for the mission extended through November 10,2008, Phoenix was NASAs sixth successful landing out of seven attempts and was the first successful landing in a Martian polar region. The lander completed its mission in August 2008, and made a last brief communication with Earth on November 2 as available solar power dropped with the Martian winter, the mission was declared concluded on November 10,2008, after engineers were unable to re-contact the craft. After unsuccessful attempts to contact the lander by the Mars Odyssey orbiter up to and past the Martian summer solstice on May 12,2010, the program was considered a success because it completed all planned science experiments and observations. One was to study the history of water, the key to unlocking the story of past climate change. The second was to evaluate past or potential planetary habitability in the ice-soil boundary, Phoenixs instruments were suitable for uncovering information on the geological and possibly biological history of the Martian Arctic. Phoenix was the first mission to return data from either of the poles, the primary mission was anticipated to last 90 sols – just over 92 Earth days. However, the craft exceeded its expected operational lifetime by a little over two months before succumbing to the cold and dark of an advancing Martian winter. Even had it survived some of the winter, the cold would have prevented it from lasting all the way through. The 2003–2004 observations of gas on Mars were made remotely by three teams working with separate data. Methane could also be the product of a process or the result of volcanic or hydrothermal activity. The mission was funded on the expectation that Phoenix would find water ice on the arctic plains of Mars. In August 2003 NASA selected the University of Arizona Phoenix mission for launch in 2007 and it was hoped this would be the first in a new line of smaller, low-cost, Scout missions in the agencys exploration of Mars program. The selection was the result of an intense competition with proposals from other institutions. The $325 million NASA award is more than six times larger than any single research grant in University of Arizona history
18.
Mars Science Laboratory
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Mars Science Laboratory is a robotic space probe mission to Mars launched by NASA on November 26,2011, which successfully landed Curiosity, a Mars rover, in Gale Crater on August 6,2012. The overall objectives include investigating Mars habitability, studying its climate and geology, the rover carries a variety of scientific instruments designed by an international team. MSL successfully carried out the most accurate Martian landing of any spacecraft, hitting a small target landing ellipse of only 7 by 20 km. In the event, MSL achieved a landing 2.4 km east and 400 m north of the center of the target and this location is near the mountain Aeolis Mons. The rover mission is set to explore for at least 687 Earth days over a range of 5 by 20 km, the total cost of the MSL project is about US$2.5 billion. Mars rovers include Sojourner from the Mars Pathfinder mission and the Mars Exploration Rovers Spirit, Curiosity is about twice as long and five times as heavy as Spirit and Opportunity, and carries over ten times the mass of scientific instruments. The MSL mission has four scientific goals, Determine the landing sites habitability including the role of water, the study of the climate and it is also useful preparation for a future manned mission to Mars. This data would be important for a manned mission. The MSL spacecraft includes spaceflight-specific instruments, in addition to utilizing one of the rover instruments—Radiation assessment detector —during the spaceflight transit to Mars. MSL EDL Instrument, The MEDLI projects main objective is to measure aerothermal environments, sub-surface heat shield material response, vehicle orientation, the MEDLI instrumentation suite was installed in the heatshield of the MSL entry vehicle. The acquired data will support future Mars missions by providing measured atmospheric data to validate Mars atmosphere models, MEDLI instrumentation consists of three main subsystems, MEDLI Integrated Sensor Plugs, Mars Entry Atmospheric Data System and the Sensor Support Electronics. Each computers memory includes 256 KB of EEPROM,256 MB of DRAM and this compares to 3 MB of EEPROM,128 MB of DRAM, and 256 MB of flash memory used in the Mars Exploration Rovers. The RCE computers use the RAD750 CPU operating at 200 MHz, the RAD750 CPU is capable of up to 400 MIPS, while the RAD6000 CPU is capable of up to 35 MIPS. Of the two computers, one is configured as backup, and will take over in the event of problems with the main computer. The rover has an Inertial Measurement Unit that provides 3-axis information on its position, the rovers computers are constantly self-monitoring to keep the rover operational, such as by regulating the rovers temperature. Activities such as taking pictures, driving, and operating the instruments are performed in a sequence that is sent from the flight team to the rover. The rovers computers function on VxWorks, an operating system from Wind River Systems. Once landed, the applications were replaced with software for driving on the surface, communications, Curiosity is equipped with several means of communication, for redundancy
19.
Solar panel
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Solar panel refers to a panel designed to absorb the suns rays as a source of energy for generating electricity or heating. A photovoltaic module is a packaged, connect assembly of typically 6×10 photovoltaic solar cells, photovoltaic modules constitute the photovoltaic array of a photovoltaic system that generates and supplies solar electricity in commercial and residential applications. Each module is rated by its DC output power under standard test conditions, the efficiency of a module determines the area of a module given the same rated output – an 8% efficient 230 watt module will have twice the area of a 16% efficient 230 watt module. There are a few commercially available solar modules that exceed 22% efficiency, a single solar module can produce only a limited amount of power, most installations contain multiple modules. A photovoltaic system typically includes an array of photovoltaic modules, an inverter, a pack for storage, interconnection wiring. The most common application of solar panels is solar heating systems. The price of power has continued to fall so that in many countries it is cheaper than ordinary fossil fuel electricity from the grid. Photovoltaic modules use light energy from the Sun to generate electricity through the photovoltaic effect, the majority of modules use wafer-based crystalline silicon cells or thin-film cells. The structural member of a module can either be the top layer or the back layer, cells must also be protected from mechanical damage and moisture. Most modules are rigid, but semi-flexible ones are available, based on thin-film cells, the cells must be connected electrically in series, one to another. Externally, most of photovoltaic modules use MC4 connectors type to facilitate easy connections to the rest of the system. Modules electrical connections are made in series to achieve an output voltage and/or in parallel to provide a desired current capability. The conducting wires that take the current off the modules may contain silver, copper or other non-magnetic conductive transition metals, bypass diodes may be incorporated or used externally, in case of partial module shading, to maximize the output of module sections still illuminated. Some special solar PV modules include concentrators in which light is focused by lenses or mirrors onto smaller cells and this enables the use of cells with a high cost per unit area in a cost-effective way. Depending on construction, photovoltaic modules can produce electricity from a range of frequencies of light, hence, much of the incident sunlight energy is wasted by solar modules, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into different wavelength ranges and this has been projected to be capable of raising efficiency by 50%. Scientists from Spectrolab, a subsidiary of Boeing, have reported development of solar cells with an efficiency of more than 40%. Currently the best achieved sunlight conversion rate is around 21. 5% in new products typically lower than the efficiencies of their cells in isolation
20.
Spacecraft
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A spacecraft is a vehicle, or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, on a sub-orbital spaceflight, a spacecraft enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies, robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a body are artificial satellites. Only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, orbital spacecraft may be recoverable or not. By method of reentry to Earth they may be divided in non-winged space capsules, Sputnik 1 was the first artificial satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957, the launch ushered in new political, military, technological, and scientific developments, while the Sputnik launch was a single event, it marked the start of the Space Age. Apart from its value as a technological first, Sputnik 1 also helped to identify the upper atmospheric layers density and it also provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen in the satellites false body provided the first opportunity for meteoroid detection, Sputnik 1 was launched during the International Geophysical Year from Site No. 1/5, at the 5th Tyuratam range, in Kazakh SSR. The satellite travelled at 29,000 kilometers per hour, taking 96.2 minutes to complete an orbit and this altitude is called the Kármán line. In particular, in the 1940s there were several test launches of the V-2 rocket, as of 2016, only three nations have flown manned spacecraft, USSR/Russia, USA, and China. The first manned spacecraft was Vostok 1, which carried Soviet cosmonaut Yuri Gagarin into space in 1961, there were five other manned missions which used a Vostok spacecraft. The second manned spacecraft was named Freedom 7, and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers, there were five other manned missions using Mercury spacecraft. Other Soviet manned spacecraft include the Voskhod, Soyuz, flown unmanned as Zond/L1, L3, TKS, China developed, but did not fly Shuguang, and is currently using Shenzhou. Except for the shuttle, all of the recoverable manned orbital spacecraft were space capsules. Manned space capsules The International Space Station, manned since November 2000, is a joint venture between Russia, the United States, Canada and several other countries, some reusable vehicles have been designed only for manned spaceflight, and these are often called spaceplanes. The first example of such was the North American X-15 spaceplane, the first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19,1963. The first partially reusable spacecraft, a winged non-capsule, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarins flight
21.
Temperature
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A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, geology, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale. Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, nevertheless, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials
22.
Analemma
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In astronomy, an analemma is a diagram showing the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth. Due to the Earths axial tilt and orbital eccentricity, the Sun will not be in the position in the sky at the same time every day. The north–south component of the analemma is the Suns declination, and this diagram has the form of a slender figure-eight, and can often be found on globes of the Earth. Diagrams of analemmas frequently carry marks that show the position of the Sun at various closely spaced throughout the year. Analemmas with date marks can be used for practical purposes. Without date marks, they are of use, except as decoration. Analemmas have been used in conjunction with sundials since the 18th century to convert between apparent and mean solar time, prior to this, the term referred to any tool or method used in the construction of sundials. It is possible to photograph the analemma by keeping a camera at a location and orientation and taking multiple exposures throughout the year. Although the term usually refers to the Earths solar analemma. The resulting curve resembles a long, slender figure-eight with one much larger than the other. This curve is commonly printed on terrestrial globes, usually in the eastern Pacific Ocean, the only large tropical region with very little land. It is possible, though challenging, to photograph the analemma, by leaving the camera in a position for an entire year and snapping images on 24-hour intervals. The component along this axis of the Suns apparent motion is a result of the seasonal variation of the declination of the Sun through the year. e. This width of the analemma is approximately 7. 7°, so the length of the figure is more than six times its width. The figure-eight form arises from the relationship between the direction of the Earths axis, and the passing through the perihelion and aphelion of the Earths elliptical orbit around the Sun. There are three parameters that affect the size and shape of the analemma — obliquity, eccentricity, for an object with a circular orbit but significant axial tilt, the analemma would be a figure of eight with northern and southern lobes equal in size. For an object with an eccentric orbit but no axial tilt, the north–south component of the analemma shows the Suns declination, its latitude on the celestial sphere, or the latitude on the Earth at which the Sun is directly overhead. The east–west component shows the equation of time, or the difference between time and local mean time
23.
Equation of time
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The equation of time describes the discrepancy between two kinds of solar time. The word equation is used in the sense of reconcile a difference. The two times that differ are the apparent solar time, which tracks the motion of the sun, and mean solar time. Apparent solar time can be obtained by measurement of the current position of the Sun, Mean solar time, for the same place, would be the time indicated by a steady clock set so that over the year its differences from apparent solar time would resolve to zero. The equation of time is the east or west component of the analemma, the equation of time values for each day of the year, compiled by astronomical observatories, were widely listed in almanacs and ephemerides. During a year the equation of time varies as shown on the graph, apparent time, and the sundial, can be ahead by as much as 16 min 33 s, or behind by as much as 14 min 6 s. The equation of time has zeros near 15 April,13 June,1 September and 25 December, ignoring very slow changes in the Earths orbit and rotation, these events are repeated at the same times every tropical year. However, due to the number of days in a year. The equation of time is constant only for a planet with zero axial tilt, on Mars the difference between sundial time and clock time can be as much as 50 minutes, due to the considerably greater eccentricity of its orbit. The planet Uranus, which has a large axial tilt, has an equation of time that makes its days start. There is no accepted definition of the sign of the equation of time. Some publications show it as positive when a sundial is ahead of a clock, as shown in the graph above, others when the clock is ahead of the sundial. In the English-speaking world, the usage is the more common. Anyone who makes use of a table or graph should first check its sign usage. Often, there is a note or caption which explains it, otherwise, the sign can be determined by knowing that, during the first three months of each year, the clock is ahead of the sundial. The mnemonic NYSS, for new year, sundial slow, can be useful, some published tables avoid the ambiguity by not using signs, but by showing phrases such as sundial fast or sundial slow instead. In this article, and others in English Wikipedia, a value of the equation of time implies that a sundial is ahead of a clock. The phrase equation of time is derived from the medieval Latin, the word aequātiō was widely used in early astronomy to tabulate the difference between an observed value and the expected value
24.
Prime meridian
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A prime meridian is a meridian in a geographical coordinate system at which longitude is defined to be 0°. Together, a meridian and its antimeridian form a great circle. This great circle divides the sphere, e. g. the Earth, if one uses directions of East and West from a defined prime meridian, then they can be called Eastern Hemisphere and Western Hemisphere. The most widely used modern meridian is the IERS Reference Meridian and it is derived but deviates slightly from the Greenwich Meridian, which was selected as an international standard in 1884. The notion of longitude was developed by the Greek Eratosthenes in Alexandria, and Hipparchus in Rhodes, but it was Ptolemy who first used a consistent meridian for a world map in his Geographia. The main point is to be comfortably west of the tip of Africa as negative numbers were not yet in use. His prime meridian corresponds to 18°40 west of Winchester today, at that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries. Ptolemys Geographia was first printed with maps at Bologna in 1477, but there was still a hope that a natural basis for a prime meridian existed. The Tordesillas line was settled at 370 leagues west of Cape Verde. This is shown in Diogo Ribeiros 1529 map, in 1541, Mercator produced his famous 41 cm terrestrial globe and drew his prime meridian precisely through Fuertaventura in the Canaries. His later maps used the Azores, following the magnetic hypothesis, but by the time that Ortelius produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today and this practice was followed by navigators well into the 18th century. In 1634, Cardinal Richelieu used the westernmost island of the Canaries, Ferro, 19°55 west of Paris, the geographer Delisle decided to round this off to 20°, so that it simply became the meridian of Paris disguised. In the early 18th century the battle was on to improve the determination of longitude at sea, between 1765 and 1811, Nevil Maskelyne published 49 issues of the Nautical Almanac based on the meridian of the Royal Observatory, Greenwich. Maskelynes tables not only made the lunar method practicable, they made the Greenwich meridian the universal reference point. In 1884, at the International Meridian Conference in Washington, D. C.22 countries voted to adopt the Greenwich meridian as the meridian of the world. The French argued for a line, mentioning the Azores and the Bering Strait. In October 1884 the Greenwich Meridian was selected by delegates to the International Meridian Conference held in Washington, united States to be the common zero of longitude and standard of time reckoning throughout the world
25.
Airy-0
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Airy-0 is a crater on Mars whose location defines the position of the prime meridian of that planet. It is about 0.5 kilometres across and lies within the larger crater Airy in the region Sinus Meridiani and it was named in honor of the British Astronomer Royal Sir George Biddell Airy, who in 1850 built the transit circle telescope at Greenwich. The location of that telescope was subsequently chosen to define the location of Earths prime meridian, merton Davies chose this crater as Marss prime meridian in 1969 based on Mariner 6 and 7 photographs. View of Airy-0 at Google Mars The Martian Prime Meridian Where is zero degrees longitude on Mars
26.
Mars Exploration Rovers
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NASAs Mars Exploration Rover mission is an ongoing robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars. It began in 2003 with the sending of the two rovers, MER-A Spirit and MER-B Opportunity—to explore the Martian surface and geology, both rovers outlived their planned missions of 90 Martian solar days by far. MER-A Spirit was active until 2010, the success of the two MERs led to another mission, sending a bigger rover Curiosity in 2012. The missions scientific objective was to search for and characterize a wide range of rocks, the mission is part of NASAs Mars Exploration Program, which includes three previous successful landers, the two Viking program landers in 1976 and Mars Pathfinder probe in 1997. The total cost of building, launching, landing and operating the rovers on the surface for the initial 90-sol primary mission was US$820 million, since the rovers have continued to function beyond their initial 90 sol primary mission, they have each received five mission extensions. The fifth mission extension was granted in October 2007, and ran to the end of 2009, the total cost of the first four mission extensions was $104 million, and the fifth mission extension is expected to cost at least $20 million. However, the dust storms lifted, allowing them to resume operations, on May 1,2009, during its fifth mission extension, Spirit became stuck in soft soil on Mars. This mode would enable Spirit to assist scientists in ways that a mobile platform could not, in recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honor,37452 Spirit and 39382 Opportunity. The mission is managed for NASA by the Jet Propulsion Laboratory, which designed, built, the search for evidence of habitability, taphonomy, and organic carbon on the planet Mars is now a primary NASA objective. The scientific objectives of the Mars Exploration Rover mission are to, Search for and characterize a variety of rocks, in particular, samples sought include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity. Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites, determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, perform calibration and validation of surface observations made by Mars Reconnaissance Orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit, Search for iron-containing minerals, and to identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates. Characterize the mineralogy and textures of rocks and soils to determine the processes that created them, Search for geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life, the MER-A and MER-B probes were launched on June 10,2003 and July 7,2003, respectively. The launch vehicles were integrated onto pads right next to other, with MER-A on CCAFS SLC-17A. The dual pads allowed for working the 15- and 21-day planetary launch periods close together, the last possible day for MER-A was June 19,2003. NASAs Launch Services Program managed the launch of both spacecraft, the probes landed in January 2004 in widely separated equatorial locations on Mars
27.
Planetocentric longitude
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Longitude, is a geographic coordinate that specifies the east-west position of a point on the Earths surface. It is a measurement, usually expressed in degrees and denoted by the Greek letter lambda. Meridians connect points with the same longitude, by convention, one of these, the Prime Meridian, which passes through the Royal Observatory, Greenwich, England, was allocated the position of zero degrees longitude. The longitude of places is measured as the angle east or west from the Prime Meridian, ranging from 0° at the Prime Meridian to +180° eastward. Specifically, it is the angle between a plane containing the Prime Meridian and a plane containing the North Pole, South Pole and the location in question. A locations north–south position along a meridian is given by its latitude, everywhere on Earth the vertical north–south plane would contain the Earths axis. But the Earth is not homogeneous, and has mountains—which have gravity, the vertical north–south plane still intersects the plane of the Greenwich meridian at some angle, that angle is the astronomical longitude, calculated from star observations. The measurement of longitude is important both to cartography and for ocean navigation, mariners and explorers for most of history struggled to determine longitude. Finding a method of determining longitude took centuries, resulting in the history of recording the effort of some of the greatest scientific minds. Latitude was calculated by observing with quadrant or astrolabe the altitude of the sun or of charted stars above the horizon, I compared my observations with an almanac. I found that. at midnight Marss position was three and a half degrees to the east, by comparing the positions of the moon and Mars with their anticipated positions, Vespucci was able to crudely deduce his longitude. But this method had several limitations, First, it required the occurrence of an astronomical event. One needed also to know the time, which was difficult to ascertain in foreign lands. Finally, it required a stable viewing platform, rendering the technique useless on the deck of a ship at sea. In 1714 the British government passed the Longitude Act which offered financial rewards to the first person to demonstrate a practical method for determining the longitude of a ship at sea. These rewards motivated many to search for a solution, though the Board of Longitude rewarded John Harrison for his marine chronometer in 1773, chronometers remained very expensive and the lunar distance method continued to be used for decades. Finally, the combination of the availability of chronometers and wireless telegraph time signals put an end to the use of lunars in the 20th century. Unlike latitude, which has the equator as a starting position
28.
UT1
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Universal Time is a time standard based on Earths rotation. It is a continuation of Greenwich Mean Time, i. e. the mean solar time on the Prime Meridian at Greenwich, London. In fact, the expression Universal Time is ambiguous, as there are versions of it. All of these versions of UT, except for UTC, are based on Earths rotation relative to distant celestial objects, UTC is based on International Atomic Time, with leap seconds added to keep it within 0.9 second of UT1. Prior to the introduction of time, each municipality throughout the civilized world set its official clock, if it had one. Greenwich Mean Time, where all clocks in Britain were set to the time, was established to solve this problem. Chronometers or telegraphy were used to synchronize these clocks, Standard time, as originally proposed by Scottish-Canadian Sir Sandford Fleming in 1879, divided the world into twenty-four time zones, each one covering 15 degrees of longitude. All clocks within each zone would be set to the time as the others. This location was chosen because by 1884 two-thirds of all nautical charts, the conference did not adopt Flemings time zones because they were outside the purpose for which it was called, which was to choose a basis for universal time. During the period between 1848 and 1972, all of the countries adopted time zones based on the Greenwich meridian. The term Greenwich Mean Time persists, however, in usage to this day in reference to civil timekeeping. Based on the rotation of the Earth, time can be measured by observing celestial bodies crossing the meridian every day. Astronomers found that it was accurate to establish time by observing stars as they crossed a meridian rather than by observing the position of the Sun in the sky. Nowadays, UT in relation to International Atomic Time is determined by Very Long Baseline Interferometry observations of distant quasars, the rotation of the Earth and UT are monitored by the International Earth Rotation and Reference Systems Service. The International Astronomical Union also is involved in setting standards, the rotation of the Earth is somewhat irregular, and is very gradually slowing due to tidal acceleration. Furthermore, the length of the second was determined from observations of the Moon between 1750 and 1890. All of these cause the mean solar day, on the average, to be slightly longer than the nominal 86,400 SI seconds. As UT is slightly irregular in its rate, astronomers introduced Ephemeris Time, thus, civil broadcast standards for time and frequency usually follow International Atomic Time closely, but occasionally step in order to prevent them from drifting too far from mean solar time
29.
Wilhelm Beer
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Wilhelm Wolff Beer was a banker and astronomer from Berlin, Prussia, and the half-brother of Giacomo Meyerbeer. Beers fame derives from his hobby, astronomy and he built a private observatory with a 9.5 cm refractor in Tiergarten, Berlin. Together with Johann Heinrich Mädler he produced the first exact map of the Moon in 1834-1836, both remained the best descriptions of the Moon for many decades. In 1830, Beer and Mädler created the first globe of the planet Mars. In 1840 they made a map of Mars and calculated its period to be 24 h 37 min 22.7 s. In addition to his hobby of astronomy, he helped with the establishment of a system in Prussia. In his last decade of life, he worked as a writer, in 1849 he was elected as an MP for the first chamber of the Prussian parliament. The crater Beer on Mars is named in Wilhelm Beers honor and lies near Mädler
30.
Sinus Meridiani
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Sinus Meridiani is a feature name for an albedo feature on Mars stretching east-west just south of that planets equator. It was named by the French astronomer Camille Flammarion in the late 1870s and it has a diameter of 1622 km, and its center is located at 7.12 S and 4 E. The name Sinus Meridiani was given to the a classic albedo feature on Mars by the French astronomer Camille Flammarion in the late 1870s, however, the older and the newer designations are both in current use. The U. S. Geological Survey considers the Sinus Meridiani nomenclature canonical. The name Meridiani Planum is used to specifically to the landing site of Mars Exploration Rover Opportunity. It was decided that the spectra signal spotted from orbit by Mars Odyssey was produced by these spherules, after further study it was decided that the blueberries were concretions formed in the ground by water. Over time, these concretions weathered from what was overlying rock, the concentration of spherules in bedrock could have produced the observed blueberry covering from the weathering of as little as one meter of rock. Most of the soil consisted of olivine basalt sands that did not come from the local rocks, the sand may have been transported from somewhere else. A Mössbauer spectrum was made of the dust that gathered on Opportunity’s capture magnet, the results suggested that the magnetic component of the dust was titanomagnetite, rather than just plain magnetite, as was once thought. A small amount of olivine was also detected which was interpreted as indicating a long period on the planet. On the other hand, an amount of hematite that was present meant that there may have been liquid water for a short time in the early history of the planet. Because the Rock Abrasion Tool found it easy to grind into the bedrocks, few rocks were visible on the surface where Opportunity landed, but bedrock that was exposed in craters was examined by the suite of instruments on the Rover. Bedrock rocks were found to be sedimentary rocks with a concentration of sulfur in the form of calcium and magnesium sulfates. Some of the sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, salts, such as halite, bischofite, antarcticite, bloedite, vanthoffite, or gluberite may also be present. The rocks contained the sulfates had a light tone compared to isolated rocks and rocks examined by landers/rovers at other locations on Mars. The spectra of these light toned rocks, containing hydrated sulfates, were similar to spectra taken by the Thermal Emission Spectrometer on board the Mars Global Surveyor. The same spectrum is found over an area, so it is believed that water once appeared over a wide region. The Alpha Particle X-ray Spectrometer found rather high levels of phosphorus in the rocks, similar high levels were found by other rovers at Ares Vallis and Gusev Crater, so it has been hypothesized that the mantle of Mars may be phosphorus-rich
31.
Giovanni Schiaparelli
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Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He was educated at the University of Turin, and later studied at Berlin Observatory, in 1859–1860 he worked in Pulkovo Observatory near St Petersburg, and then worked for over forty years at Brera Observatory in Milan. Among Schiaparellis contributions are his telescopic observations of Mars, in his initial observations, he named the seas and continents of Mars. While the term indicates an artificial construction, the term channels connotes that the observed features were natural configurations of the planetary surface. Later, with thanks to the observations of the Italian astronomer Vincenzo Cerulli. I have already pointed out that, in the absence of rain on Mars and he proved, for example, that the orbit of the Leonid meteor shower coincided with that of the comet Tempel-Tuttle. These observations led the astronomer to formulate the hypothesis, subsequently proved to be correct and he was also a keen observer of the inner planets Mercury and Venus. He made several drawings and determined their rotation periods, in 1965, it was shown that his and most other subsequent measurements of Mercurys period were incorrect. Schiaparelli was a scholar of the history of classical astronomy, lalande Prize Gold Medal of the Royal Astronomical Society Bruce Medal The main-belt asteroid 4062 Schiaparelli, named on 15 September 1989. The lunar crater Schiaparelli The Martian crater Schiaparelli Schiaparelli Dorsum on Mercury The 2016 ExoMars Schiaparelli lander and his niece, Elsa Schiaparelli, became a noted designer or maker of haute couture. 1873 – Le stelle cadenti 1893 – La vita sul pianeta Marte 1925 – Scritti sulla storia della astronomia antica in three volumes, Schiaparelli, Giovanni Virginio, biography from www. daviddarling. info. Obituaries, G. V. Schiaparelli, J. G. Galle, J. B. N. Hennessey J. Coles, J. E. Gore, The Observatory, Vol.33, p. 311–318, August 1910 Source texts from Wikisource in Italian and English. Le Mani su Marte, I diari di G. V, Works by Giovanni Virginio Schiaparelli at Project Gutenberg Works by or about Giovanni Schiaparelli at Internet Archive AN185 193/194 ApJ32313 MNRAS71282 PASP22164
32.
International Meridian Conference
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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
33.
Coordinated Universal Time
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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
34.
Leap second
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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
35.
Goddard Institute for Space Studies
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The Goddard Institute for Space Studies is a laboratory in the Earth Sciences Division of NASAs Goddard Space Flight Center and a unit of the Columbia University Earth Institute. The institute is located at Columbia University in New York City, research at the GISS emphasizes a broad study of Global Change, the natural and anthropogenic changes in our environment that affect the habitability of our planet. These effects may occur on greatly differing time scales, from one-time forcings such as explosions, to seasonal/annual effects such as El Niño. The Institutes research combines analysis of comprehensive global datasets, with models of atmospheric, land surface. Study of past climate change on Earth and of other planetary atmospheres provides a tool in assessing our general understanding of the atmosphere. GISS was established in May 1961 by Robert Jastrow to do research in space sciences in support of Goddard programs. Soon enough it became known as the Goddard Institute for Space Studies and it was separated from the Theoretical Division in July 1962. Its offices were located in The Interchurch Center, and the institute moved into Columbias Armstrong Hall in April 1966. From 1981 to 2013, GISS was directed by James E. Hansen, in June 2014, Gavin A. Schmidt was named the institutes third director. At a GISS workshop in 1967, John Wheeler popularized the term black hole as a short-hand for gravitionally completely collapsed star, though the term was not coined there. In November 2004, Climatologists Drew Shindell and Gavin Schmidt of NASAs Goddard Institute for Space Studies, New York, a key objective of Goddard Institute for Space Studies research is prediction of climate change in the 21st century. The research combines paleogeological record, analysis of comprehensive global datasets, with models of atmospheric, land surface. Climate science predictions are based substantially on historical analysis of Earths paleoclimate, changes in carbon dioxide associated with continental drift, and the decrease in volcanism as India arrived at the Asian continent, allowed temperatures to drop & Antarctic ice-sheets to form. This resulted in a 75m drop in sea level, allowing our present-day coastlines & habitats to form, the institute is housed at the corner of West 112th St. and Broadway in New York City in Columbia Universitys Armstrong Hall. The building also houses Toms Restaurant, which was the exterior for the restaurant in Seinfeld and the subject of the Suzanne Vega song Toms Diner
36.
Greenwich Mean Time
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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
37.
United States Geological Survey
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The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its resources. The organization has four science disciplines, concerning biology, geography, geology. The USGS is a research organization with no regulatory responsibility. The USGS is a bureau of the United States Department of the Interior, the USGS employs approximately 8,670 people and is headquartered in Reston, Virginia. The USGS also has major offices near Lakewood, Colorado, at the Denver Federal Center, the current motto of the USGS, in use since August 1997, is science for a changing world. The agencys previous slogan, adopted on the occasion of its anniversary, was Earth Science in the Public Service. Prompted by a report from the National Academy of Sciences, the USGS was created, by a last-minute amendment and it was charged with the classification of the public lands, and examination of the geological structure, mineral resources, and products of the national domain. This task was driven by the need to inventory the vast lands added to the United States by the Louisiana Purchase in 1803, the legislation also provided that the Hayden, Powell, and Wheeler surveys be discontinued as of June 30,1879. Clarence King, the first director of USGS, assembled the new organization from disparate regional survey agencies, after a short tenure, King was succeeded in the directors chair by John Wesley Powell. Administratively, it is divided into a Headquarters unit and six Regional Units, Other specific programs include, Earthquake Hazards Program monitors earthquake activity worldwide. The National Earthquake Information Center in Golden, Colorado on the campus of the Colorado School of Mines detects the location, the USGS also runs or supports several regional monitoring networks in the United States under the umbrella of the Advanced National Seismic System. The USGS informs authorities, emergency responders, the media, and it also maintains long-term archives of earthquake data for scientific and engineering research. It also conducts and supports research on long-term seismic hazards, USGS has released the UCERF California earthquake forecast. The USGS National Geomagnetism Program monitors the magnetic field at magnetic observatories and distributes magnetometer data in real time, the USGS operates the streamgaging network for the United States, with over 7400 streamgages. Real-time streamflow data are available online, since 1962, the Astrogeology Research Program has been involved in global, lunar, and planetary exploration and mapping. USGS operates a number of related programs, notably the National Streamflow Information Program. USGS Water data is available from their National Water Information System database
38.
Mars Phoenix
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Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25,2008, Mission scientists used instruments aboard the lander to search for environments suitable for microbial life on Mars, and to research the history of water there. The total mission cost was about US $386 million, which includes cost of the launch, the multi-agency program was headed by the Lunar and Planetary Laboratory at the University of Arizona, under the direction of NASAs Jet Propulsion Laboratory. It was the first mission to Mars led by a university in NASA history. The operational funding for the mission extended through November 10,2008, Phoenix was NASAs sixth successful landing out of seven attempts and was the first successful landing in a Martian polar region. The lander completed its mission in August 2008, and made a last brief communication with Earth on November 2 as available solar power dropped with the Martian winter, the mission was declared concluded on November 10,2008, after engineers were unable to re-contact the craft. After unsuccessful attempts to contact the lander by the Mars Odyssey orbiter up to and past the Martian summer solstice on May 12,2010, the program was considered a success because it completed all planned science experiments and observations. One was to study the history of water, the key to unlocking the story of past climate change. The second was to evaluate past or potential planetary habitability in the ice-soil boundary, Phoenixs instruments were suitable for uncovering information on the geological and possibly biological history of the Martian Arctic. Phoenix was the first mission to return data from either of the poles, the primary mission was anticipated to last 90 sols – just over 92 Earth days. However, the craft exceeded its expected operational lifetime by a little over two months before succumbing to the cold and dark of an advancing Martian winter. Even had it survived some of the winter, the cold would have prevented it from lasting all the way through. The 2003–2004 observations of gas on Mars were made remotely by three teams working with separate data. Methane could also be the product of a process or the result of volcanic or hydrothermal activity. The mission was funded on the expectation that Phoenix would find water ice on the arctic plains of Mars. In August 2003 NASA selected the University of Arizona Phoenix mission for launch in 2007 and it was hoped this would be the first in a new line of smaller, low-cost, Scout missions in the agencys exploration of Mars program. The selection was the result of an intense competition with proposals from other institutions. The $325 million NASA award is more than six times larger than any single research grant in University of Arizona history
39.
Carl Otto Lampland
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Carl Otto Lampland was an American astronomer. He was born into a family of ten children, both his father Ole Helliksen Lampland and his mother Berit Gulliksdatter Skartum were born in Norway. He was educated first at Valparaiso Normal school in Valparaiso, Indiana and he then studied at Indiana University, where he received a B. A. degree in astronomy in 1902, an M. A. in 1906, and an honorary LL. D in 1930. He first went to Lowell Observatory in 1902 when invited by Percival Lowell and he designed cameras used for astronomy and also designed and maintained telescopes, including resilvering the mirror of the 40-inch telescope. He also constructed thermocouples and used them to temperatures of planets. He won the Royal Photographic Society Medal in 1905 for the camera which he designed for the 24-inch Clark telescope, together with William Coblentz, he measured large differences between the day and night temperatures on Mars which implied a thin Martian atmosphere. He discovered the asteroid 1604 Tombaugh, in 1907 Lampland and Lowell won a Royal Photographic Society exhibition medal for their photographs of Mars. His date of birth is the point for the Mars Sol Date calendar. The lunar crater Lampland as well as the Martian crater Lampland were named after him, the main-belt asteroid 1767 Lampland is also named after him. Lampland Collection in maintained at the Lowell Observatory Archives in Flagstaff
40.
Telescope
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A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
