International Date Line
The International Date Line is an imaginary line of demarcation on the surface of Earth that runs from the North Pole to the South Pole and demarcates the change of one calendar day to the next. It passes through the middle of the Pacific Ocean following the 180° line of longitude but deviating to pass around some territories and island groups; this description is based on the most common understanding of the de facto International Date Line. See § De facto and de jure date lines below, map above at right; the IDL is based on the meridian of 180° longitude down the middle of the Pacific Ocean, halfway around the world from the Greenwich meridian. In many places, the IDL follows the 180° meridian exactly. In other places, the IDL deviates east or west away from that meridian; these various deviations accommodate the political and/or economic affiliations of the affected areas. Proceeding from north to south, the first deviation of the IDL from 180° is to pass to the east of Wrangel Island and the Chukchi Peninsula, the easternmost part of Russian Siberia.
It passes through the Bering Strait between the Diomede Islands at a distance of 1.5 kilometres from each island at 168°58′37″ W. It bends west of 180°, passing west of St. Lawrence Island and St. Matthew Island; the IDL crosses between the U. S. Aleutian Islands and the Commander Islands, which belong to Russia, it bends southeast again to return to 180°. Thus, all of Russia is to the west of the IDL, all of the United States is to the east except for the insular areas of Guam, the Northern Mariana Islands, Wake Island; the IDL remains on the 180° meridian until passing the equator. Two US-owned uninhabited atolls, Howland Island and Baker Island, just north of the equator in the central Pacific Ocean, have the latest time on Earth; the IDL circumscribes Kiribati by swinging far to the east reaching the 150°W meridian. Kiribati's easternmost islands, the southern Line Islands south of Hawaii, have the most advanced time on Earth, UTC+14:00 hours. South of Kiribati, the IDL returns westwards but remains east of 180°, passing between Samoa and American Samoa.
In much of this area, the IDL follows the 165°W meridian. Accordingly, Tokelau and Futuna, Tonga and New Zealand's Kermadec Islands and Chatham Islands are all west of the IDL and have the same date. American Samoa, the Cook Islands and French Polynesia are east of the IDL and one day behind; the IDL bends southwest to return to 180°. It follows that meridian until reaching Antarctica. Conventionally, the IDL is not drawn into Antarctica on most maps. A person who goes around the world from east to west would gain or set their clock back one hour for every 15° of longitude crossed, would gain 24 hours for one circuit of the globe from east to west if they did not compensate by setting their clock forward one day when they crossed the IDL. In contrast, a west-to-east circumnavigation of the globe loses an hour for every 15° of longitude crossed but gains back a day when crossing the IDL; the IDL must therefore be observed in conjunction with the Earth's time zones: on crossing it in either direction, the calendar date is adjusted by one day.
For the two hours between 10:00 and 11:59 UTC each day, three different calendar dates are observed at the same time in different places on Earth. For example, at 10:15 UTC Thursday, it is 23:15 Wednesday in American Samoa, Thursday in most of the world, 00:15 Friday in Kiritimati. During the first hour, all three calendar dates include inhabited places. During the second hour one of the calendar dates is limited to an uninhabited maritime time zone twelve hours behind UTC. According to the clock, the first areas to experience a new day and a New Year are islands that use UTC+14:00; these include portions of the Republic of Kiribati, including Millennium Island in the Line Islands, as well as Samoa during the southern summer. The first major cities to experience a new day are New Zealand. A 1994 realignment of the IDL made Caroline Island one of the first points of land on Earth to reach January 1, 2000 on the calendar; as a result, this atoll was renamed Millennium Island. The areas that are the first to see the daylight of a new day vary by the season.
Around the June solstice, the first area would be anyplace within the Kamchatka Time Zone, far enough north to experience midnight sun on the given date. At the equinoxes, the first place to see daylight would be the uninhabited Millennium Island in Kiribati, the easternmost land located west of the IDL. Near the December solstice, the first places would be Antarctic research stations using New Zealand Time during summer that experience midnight sun; these include Amundsen-Scott South Pole Station, McMurdo Station, Scott Base and Mario Zucchelli Station. There are two ways time zones and thereby the location of the International Date Line are determined, one on land and adjacent territorial waters, the other on open seas. All nations unilaterally determine their standard time zones, applicable only on land and adjacent territorial waters; this date line can be called de facto since it is not based on international law, but on national laws. These national zones do not extend into international waters.
The nautical date line, not
Western Hemisphere
The Western Hemisphere is a geographical term for the half of Earth which lies west of the prime meridian and east of the antimeridian. The other half is called the Eastern Hemisphere; the Western Hemisphere consists of the Americas, the western portions of Eurasia and Africa, the extreme eastern tip of Siberia, numerous territories in Oceania, a portion of Antarctica, while excluding some of the Aleutian Islands to the southwest of the Alaskan mainland. In an attempt to define the Western Hemisphere as the parts of the world which are not part of the Old World, there exist projections which use the 20th meridian west and the diametrically opposed 160th meridian east to define the hemisphere; this projection excludes the European and African mainlands and a small portion of northeast Greenland, but includes more of eastern Russia and Oceania. The center of the Western Hemisphere is located in the Pacific Ocean at the intersection of the 90th meridian west and the Equator, among the Galápagos Islands.
The nearest land is Genovesa Island at 0°19′00″N 89°57′00″W. The highest mountain in the Western Hemisphere is Aconcagua in the Andes of Argentina at 6,960.8 metres. Below is a list of the sovereign states which are in both the Western and Eastern Hemispheres on the IERS Reference Meridian, in order from north to south: Denmark. Norway. United Kingdom Netherlands France Spain Algeria Mali Burkina Faso Ghana TogoBelow is a list of the sovereign states which are in both the Western and Eastern Hemispheres along the 180th meridian, in order from north to south. With the exception of the United States, all of them are located on just one side of the International Date Line, curved around them. Russia United States Kiribati Tuvalu Fiji New Zealand The following countries and territories lie outside the Americas yet are entirely/mostly or within the Western Hemisphere: Media related to Western Hemisphere at Wikimedia Commons
South Magnetic Pole
The South Magnetic Pole is the wandering point on Earth's Southern Hemisphere where the geomagnetic field lines are directed vertically upwards. It should not be confused with the South Geomagnetic Pole described later. For historical reasons, the "end" of a hanging magnet that points north is itself called the "north pole" of the magnet, the other end, pointing south, is called the magnet's "south pole"; because opposite poles attract, Earth's South Magnetic Pole is physically a magnetic north pole. The South Magnetic Pole is shifting due to changes in Earth's magnetic field; as of 2005 it was calculated to lie at 64°31′48″S 137°51′36″E, placing it off the coast of Antarctica, between Adélie Land and Wilkes Land. In 2015 it lay at 64.28°S 136.59°E / -64.28. That point lies outside the Antarctic Circle. Due to polar drift, the pole is moving northwest by about 10 to 15 kilometres per year, its current distance from the actual Geographic South Pole is 2,860 km. The nearest permanent science station is Dumont d'Urville Station.
Wilkes Land contains a large gravitational mass concentration. Early unsuccessful attempts to reach the magnetic south pole included those of French explorer Dumont d'Urville, American Charles Wilkes and Briton James Clark Ross; the first calculation of the magnetic inclination to locate the magnetic South Pole was made on January 23, 1838 by the hydrographer Clément Adrien Vincendon-Dumoulin, a member of the Dumont d'Urville expedition in Antarctica and Oceania on the corvettes "L'Astrolabe" and "Zélée" in 1837-1840, which discovered Adelie Land. On 16 January 1909 three men from Sir Ernest Shackleton's Nimrod Expedition claimed to have found the South Magnetic Pole, at that time located on land, they claimed it for the British Empire. The three men began the expedition to the South Magnetic Pole in a motor car specially adapted for the cold conditions, but abandoned it when it proved useless on soft surfaces, they walked a total of 1260 miles to reach the South Magnetic Pole while pulling sledges and supplies that weighed 670 lbs.
Walking on foot across the coldest place on earth was perilous, the men faced many dangers such as falling in concealed snow crevasses and acquiring frostbite and snow-blindness. Fearing starvation, they rationed their biscuits down to the crumbs, hunted seals and penguins. However, there is now some doubt as to; the approximate position of the pole on 16 January 1909 was 72.25°S 155.15°E / -72.25. The South Magnetic Pole has been estimated by fits to global sets of data such as the World Magnetic Model and the International Geomagnetic Reference Model. For earlier years back to about 1600, the model GUFM1 is used, based on a compilation of data from ship logs. Earth's geomagnetic field can be approximated by a tilted dipole placed at the center of Earth; the South Geomagnetic Pole is the point where the axis of this best-fitting tilted dipole intersects Earth's surface in the southern hemisphere. As of 2005 it was calculated to be located at 79.74°S 108.22°E / -79.74. Because the field is not an exact dipole, the South Geomagnetic Pole does not coincide with the South Magnetic Pole.
Furthermore, the South Geomagnetic Pole is wandering for the same reason its northern magnetic counterpart wanders. North Magnetic Pole Polar alignment Australian Antarctic Division
Dominion Land Survey
The Dominion Land Survey is the method used to divide most of Western Canada into one-square-mile sections for agricultural and other purposes. It is based on the layout of the Public Land Survey System used in the United States, but has several differences; the DLS is the dominant survey method in the Prairie provinces, it is used in British Columbia along the Railway Belt, in the Peace River Block in the northeast of the province. The survey was begun in 1871, shortly after Manitoba and the North-West Territories became part of Canada, following the purchase of Rupert's Land from the Hudson’s Bay Company. Covering about 800,000 square kilometres, the survey system and its terminology are ingrained in the rural culture of the Prairies; the DLS is the world's largest survey grid laid down in a single integrated system. The first formal survey done in western Canada was by Peter Fidler in 1813; the inspiration for the Dominion Land Survey System was the plan for Manitoba to be agricultural economies.
With a large amount of European settlers arriving, Manitoba was undergoing a large change so grasslands and parklands were surveyed and farmed. The Dominion Land Survey system was developed because the farm name and field position descriptions used in northern Europe were not organized or flexible enough, the township and concession system used in eastern Canada was not satisfactory; the first meridian was chosen at 97°27′28.4″ west longitude and was established in 1869. Another 6 meridians were established after. A number of places are excluded from the survey system: these include federal lands such as Indian reserves, federal parks, air weapon ranges; the surveys do not encroach on reserves. When the Hudson's Bay Company relinquished their title to the Dominion on July 15, 1870, via the deed of surrender it received Section 8 and all of Section 26 excluding the northeast quarter; these lands were sold by the company and in 1984 they donated the remaining 5,100 acres to the Saskatchewan Wildlife Association.
The surveying of western Canada was divided into five basic surveys. Each survey's layout was different from the others; the first survey began in 1871 and ended in 1879 and covers some of southern Manitoba and a little of Saskatchewan. The second and smallest survey, in 1880, was used in only small areas of Saskatchewan; this system differs from the first survey because rather than running section lines parallel to the eastern boundary they run true north-south. The largest and most important of these surveys was the third which covers more land than all the others surveys put together; this survey began in 1881. That method of surveying is still used in Manitoba; the fourth and fifth surveys were used only in some townships in British Columbia. The reason that the Canadian government was pushing to subdivide Manitoba and Alberta was to affirm Canadian sovereignty over these lands; the United States was undergoing rapid expansion in the 1860s, the Canadian government was afraid that the Americans would expand into Canadian territory.
Canada's introduction of a railway and surveying was a means to discourage American encroachment. Sir John A. Macdonald remarked in 1870 that the Americans "are resolved to do all they can short of war, to get possession of our western territory, we must take immediate and vigorous steps to counteract them."The beginning of the Dominion Land Survey marked a new era for western Canada. Railways were making their way to the West and the population of western regions began to increase; the introduction of the survey system marked the end of the nomadic ways for the First Nations and Metis. This was a catalyst to the events of the Red River Rebellion. Being a surveyor was not easy; the hours were long, the time away from civilization was longer, the elements were unforgiving. A survey party consisted of up to 20 members, which would include a party chief, chain men, a cook, people to saw trees, a recorder, people to turn angles. All travel was either by foot. To begin surveying a party chief would have to buy $400 worth of instruments.
These instruments included an alidade, dumpy level, Gunter's chain, a solar compass or a vernier compass. The Dominion Land Survey system was proposed in 1869 by John Stoughton Dennis; the initial plan, though based on the square townships of the American Public Lands Survey System, involved 9 mile townships divided into sixty-four 800 acre sections consisting of four 200 acre lots each. Work to establish the first meridian and few township outlines began and ended in 1869 when a party of Metis symbolically stepped on a survey chain, beginning the Red River Resistance. Work resumed in 1871; the Dominion Land Survey System still differed from the Public Land System because it contained road allowances. The Dominion Land Survey was enormous. Around 178,0
Magnetic declination
Magnetic declination, or magnetic variation, is the angle on the horizontal plane between magnetic north and true north. This angle varies depending on changes over time. Somewhat more formally, Bowditch defines variation as “the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north; the angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation.”By convention, declination is positive when magnetic north is east of true north, negative when it is to the west. Isogonic lines are lines on the Earth's surface along which the declination has the same constant value, lines along which the declination is zero are called agonic lines; the lowercase Greek letter δ is used as the symbol for magnetic declination. The term magnetic deviation is sometimes used loosely to mean the same as magnetic declination, but more it refers to the error in a compass reading induced by nearby metallic objects, such as iron on board a ship or aircraft.
Magnetic declination should not be confused with magnetic inclination known as magnetic dip, the angle that the Earth's magnetic field lines make with the downward side of the horizontal plane. Magnetic declination varies both with the passage of time; as a traveller cruises the east coast of the United States, for example, the declination varies from 16 degrees west in Maine, to 6 in Florida, to 0 degrees in Louisiana, to 4 degrees east. The declination at London, UK was one degree 7 minutes west, reducing to 5' as of early 2019, as the country is quite small that figure is good for the whole, it is reducing, scientists predict that in about 2050 it will be zero. In most areas, the spatial variation reflects the irregularities of the flows deep in the Earth. Secular changes to these flows result in slow changes to the field strength and direction at the same point on the Earth; the magnetic declination in a given area may change over time as little as 2–2.5 degrees every hundred years or so, depending upon how far from the magnetic poles it is.
For a location closer to the pole like Ivujivik, the declination may change by 1 degree every three years. This may be insignificant to most travellers, but can be important if using magnetic bearings from old charts or metes in old deeds for locating places with any precision; as an example of how variation changes over time, see the two charts of the same area, surveyed 124 years apart. The 1884 chart shows a variation of 8 degrees, 20 minutes West; the 2008 chart shows 13 degrees, 15 minutes West. The magnetic declination at any particular place can be measured directly by reference to the celestial poles—the points in the heavens around which the stars appear to revolve, which mark the direction of true north and true south; the instrument used to perform this measurement is known as a declinometer. The approximate position of the north celestial pole is indicated by Polaris. In the northern hemisphere, declination can therefore be determined as the difference between the magnetic bearing and a visual bearing on Polaris.
Polaris traces a circle 0.73° in radius around the north celestial pole, so this technique is accurate to within a degree. At high latitudes a plumb-bob is helpful to sight Polaris against a reference object close to the horizon, from which its bearing can be taken. A rough estimate of the local declination can be determined from a general isogonic chart of the world or a continent, such as those illustrated above. Isogonic lines are shown on aeronautical and nautical charts. Larger-scale local maps may indicate current local declination with the aid of a schematic diagram. Unless the area depicted is small, declination may vary measurably over the extent of the map, so the data may be referred to a specific location on the map; the current rate and direction of change may be shown, for example in arcminutes per year. The same diagram may show the angle of grid north. On the topographic maps of the U. S. Geological Survey, for example, a diagram shows the relationship between magnetic north in the area concerned and true north, with a label near the angle between the MN arrow and the vertical line, stating the size of the declination and of that angle, in degrees, mils, or both.
A prediction of the current magnetic declination for a given location can be obtained online from a web page operated by the National Geophysical Data Center, a division of the National Oceanic and Atmospheric Administration of the United States. This model is built with all the information available to the map-makers at the start of the five-year period it is prepared for, it reflects a predictable rate of change, is more accurate than a map—which is months or years out of date—and never less accurate. The National Geospatial-Intelligence Agency provides source code written in C, based on the World Magnetic Model; the source code is fr
Eastern Hemisphere
The Eastern Hemisphere is a geographical term for the half of Earth, east of the prime meridian and west of the antimeridian. It is used to refer to Afro-Eurasia and Australia, in contrast with the Western Hemisphere, which includes North and South America; the Eastern Hemisphere may be called the "Oriental Hemisphere". In addition, it may be used in a cultural or geopolitical sense as a synonym for the "Old World"; the perfect circle, drawn with a line, demarcating the Eastern and Western Hemispheres must be an arbitrarily decided and published convention, unlike the equator, which divides the Northern and Southern Hemispheres. The prime meridian at 0° longitude and the antimeridian, at 180° longitude, are the conventionally accepted boundaries, since they divide eastern longitudes from western longitudes; this convention was established in 1884 at the International Meridian Conference held in Washington, D. C. where the standard time concepts of Canadian railroad engineer Sir Sandford Fleming were adopted.
The Hemispheres agreed. Portions of Western Europe, West Africa and extreme northeastern Russia are in the Western Hemisphere, divorcing it from the continents which form the touchstone for most geopolitical constructs of "the East" and "the West"; the meridians of 20°W and the diametrically opposed 160°E are used outside of matters of physics and navigation, which includes all of the European and African mainlands, but includes a small portion of northeast Greenland and excludes more of eastern Russia and Oceania. Prior to the global adoption of standard time, numerous prime meridians were decreed by various countries where time was defined by local noon; the center of the Eastern Hemisphere is located in the Indian Ocean at the intersection of the equator and the 90th meridian east, 910 km west of Indonesia in the Ninety East Ridge. The nearest land is Simeulue Island at 2°35′N 96°05′E; the land mass of the Eastern Hemisphere is larger than that of the Western Hemisphere and has a wide variety of habitats.
82% of humans live in the Eastern Hemisphere, 18% in the Western Hemisphere. East Antarctica Media related to Eastern Hemisphere at Wikimedia Commons
Prime meridian (Greenwich)
A prime meridian, based at the Royal Observatory, Greenwich, in London, was established by Sir George Airy in 1851. By 1884, over two-thirds of all ships and tonnage used it as the reference meridian on their charts and maps. In October of that year, at the behest of US President Chester A. Arthur, 41 delegates from 25 nations met in Washington, D. C. United States, for the International Meridian Conference; this conference selected the meridian passing through Greenwich as the official prime meridian due to its popularity. However, France abstained from the vote, French maps continued to use the Paris meridian for several decades. In the 18th century, London lexicographer Malachy Postlethwayt published his African maps showing the "Meridian of London" intersecting the Equator a few degrees west of the meridian and Accra, Ghana; the plane of the prime meridian is parallel to the local gravity vector at the Airy transit circle of the Greenwich observatory. The prime meridian was therefore long symbolised by a brass strip in the courtyard, now replaced by stainless steel, since 16 December 1999, it has been marked by a powerful green laser shining north across the London night sky.
Global Positioning System receivers show that the marking strip for the prime meridian at Greenwich is not at zero degrees, zero minutes, zero seconds but at 5.3 seconds of arc to the west of the meridian. In the past, this offset has been attributed to the establishment of reference meridians for space-based location systems such as WGS 84 or that errors crept into the International Time Bureau timekeeping process; the actual reason for the discrepancy is that the difference between precise GNSS coordinates and astronomically determined coordinates everywhere remains a localized gravity effect due to the deflection of the vertical. Before the establishment of a common meridian, most maritime countries established their own prime meridian passing through the country in question. In 1721, Great Britain established its own meridian passing through an early transit circle at the newly established Royal Observatory at Greenwich; the meridian was moved around 10 metres or so east on three occasions as transit circles with newer and better instruments were built, on each occasion next door to the existing one.
This was to allow uninterrupted observation during each new construction. The final meridian was established as an imaginary line from the north pole to the south pole passing through the Airy transit circle; this became Great Britain's meridian in 1851. For all practical purposes of the period, the changes as the meridian was moved went unnoticed. Transit instruments are installed to be perpendicular to the local level. In 1884, the International Meridian Conference took place to establish an internationally recognised single meridian; the meridian chosen was that which passed through the Airy transit circle at Greenwich and it became the prime meridian. At around the time of this conference, scientists were making measurements to determine the deflection of the vertical on a large scale. One might expect that plumb lines set up in various locations, if extended downward, would all pass through a single point, the centre of the Earth, but this is not the case due to the Earth being an ellipsoid, not a sphere.
The downward extended plumb lines don't all intersect the rotation axis of the Earth. To make computations feasible, scientists defined ellipsoids of revolution; the difference between the direction of a plumb line or vertical, a line perpendicular to the surface of the ellipsoid of revolution—a normal to said ellipsoid—at a particular observatory, is the deflection of the vertical. When the Airy transit circle was built, a mercury basin was used to align the telescope to the perpendicular, thus the circle was aligned with the local vertical or plumb line, deflected from the normal, or line perpendicular, to the reference ellipsoid used to define geodetic latitude and longitude in the International Terrestrial Reference Frame. While the local vertical defined at the Airy transit circle still points to the modern celestial meridian, it does not pass through the Earth's rotation axis; as a result of this, the ITRF zero meridian, defined by a plane passing through the Earth's rotation axis, is 102.478 metres to the east of the prime meridian.
A 2015 analysis by Malys et al. shows the offset between the Airy transit circle and the ITRF/WGS 84 meridians can be explained by this deflection of the vertical alone. The astronomical longitude of the Greenwich prime meridian was found to be 0.19″ ± 0.47″ East, i.e. the plane defined by the local vertical on the Greenwich prime meridian and the plane passing through the Earth's rotation axis on the ITRF zero meridian are parallel. However, the claim, found, e.g. in a BBC article that this difference between astronomical and geodetic coordinates means that any measurements of transit time across the IRTF zero meridian will occur 0.352 seconds before t
. The New Student's Reference Work. 1914.
