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IERS Reference Meridian
The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian (0° longitude) maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle which is at the latitude of the Royal Observatory, Greenwich. Thus it differs slightly from the historical Greenwich meridian. It is the reference meridian of the Global Positioning System (GPS) operated by the United States Space Force, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF). Location The most important reason for the 5.3 arcsecond offset between the IERS Reference Meridian and the Airy transit circle is that the observations with the transit circle were based on the local vertical, while the IERS Reference is a geodetic longitude, that is, the pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Countries Touching The Equator And Prime Meridian, Counting Norwegian Antarctic Territories
A country is a distinct part of the world, such as a state, nation, or other political entity. It may be a sovereign state or make up one part of a larger state. For example, the country of Japan is an independent, sovereign state, while the country of Wales is a component of a multi-part sovereign state, the United Kingdom. A country may be a historically sovereign area (such as Korea), a currently sovereign territory with a unified government (such as Senegal), or a non-sovereign geographic region associated with certain distinct political, ethnic, or cultural characteristics (such as the Basque Country). The definition and usage of the word "country" is flexible and has changed over time. ''The Economist'' wrote in 2010 that "any attempt to find a clear definition of a country soon runs into a thicket of exceptions and anomalies." Most sovereign states, but not all countries, are members of the United Nations. The largest country by area is Russia, while the smallest i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plate Tectonics
Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of ''continental drift'', an idea developed during the first decades of the 20th century. Plate tectonics came to be generally accepted by geoscientists after seafloor spreading was validated in the mid to late 1960s. Earth's lithosphere, which is the rigid outermost shell of the planet (the crust and upper mantle), is broken into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary: '' convergent'', '' divergent'', or '' transform''. Earthquakes, volcanic activity, mountain-building, and oce ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leap Second
A leap second is a one- second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time ( International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time ( UT1), which varies due to irregularities and long-term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972 and since then 27 leap seconds have been added to UTC. Because the Earth's rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of Solar time#Mean solar time, mean solar time (such as Universal Time, UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT). The coordination of time and frequency transmissions around the world began on 1 January 1960. UTC was first officially adopted as CCIR Recommendation 374, ''Standard-Frequency and Time-Signal Emissions'', in 1963, but the official abbreviation of UTC and the official English name of Coordinated Universal Time (along with the French equivalent) were not adopted until 1967. The system has been adjusted several times, including a brief period during which the time-coordination radio signals broadcast both UTC and "Stepped Atomic Time (SAT)" before a new UTC was adopted in 1970 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Universal Time
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as a modern replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship :ERA = 2π(0.7790572732640 + 1.00273781191135448'' · Tu'') radians where ''Tu'' = ( Julian UT1 date - 2451545.0). History Prior to the introduction of standard time, each municipality throughout the clock-using world set its official clock, if it had one, according to the local position of the Sun (see solar time). This served adequately until the introduction of rail travel in Britain, which made it possible to travel fast enough over long distances to require contin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eastern Hemisphere
The Eastern Hemisphere is the half of the planet Earth which is east of the prime meridian (which crosses Greenwich, London, United Kingdom) and west of the antimeridian (which crosses the Pacific Ocean and relatively little land from pole to pole). It is also used to refer to Afro-Eurasia ( Africa and Eurasia) and Australia, in contrast with the Western Hemisphere, which includes mainly North and South America. The Eastern Hemisphere may also be called the "Oriental Hemisphere", and may in addition be used in a cultural or geopolitical sense as a synonym for the " Old World." Geography The almost perfect circle (the earth is an oblate that is fatter around the equator), drawn with a line, demarcating the Eastern and Western Hemispheres must be an arbitrarily decided and published convention, unlike the Equator (an imaginary line encircling Earth, equidistant from its poles), which divides the Northern and Southern Hemispheres. The prime meridian at 0° lon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Western Hemisphere
The Western Hemisphere is the half of the planet Earth that lies west of the prime meridian (which crosses Greenwich, London, United Kingdom) and east of the antimeridian. The other half is called the Eastern Hemisphere. Politically, the term Western Hemisphere is often used as a metonymy for the Americas, even though geographically the hemisphere also includes parts of other continents. . Geography The Western Hemisphere consists of the , excluding some of the |
Great Circle
In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point. Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geometry are the natural analog of straight lines in Euclidean space. For any pair of distinct non- antipodal points on the sphere, there is a unique great circle passing through both. (Every great circle through any point also passes through its antipodal point, so there are infinitely many great circles through two antipodal points.) The shorter of the two great-circle arcs between two distinct points on the sphere is called the ''minor arc'', and is the shortest surface-path between them. Its arc length is the great-circle distance between the points (the intrinsic distance on a sphere), and is proportional to the measure of the central angle formed by the two points and the center of the sphere. A great circle is the largest circle that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prime Meridian
A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides a spheroid, like the Earth, into two hemispheres: the Eastern Hemisphere and the Western Hemisphere (for an east-west notational system). For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history. The Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Greenwich Meridian, the previous standard. A prime meridian for a planetary body not tidally locked (or at least not in synchronous rotation) is entirely arbitrary, unlike an equator, which is determined by the axis of rotation. However, for celestial objects that are tidally locked (more specifically, synchronous) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meridian (geography)
In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle (in degrees or other units) east or west of a given prime meridian (currently, the IERS Reference Meridian). In other words, it is a line of longitude. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. A meridian is half of a great circle on Earth's surface. The length of a meridian on a modern ellipsoid model of Earth ( WGS 84) has been estimated as . Pre-Greenwich The first prime meridian was set by Eratosthenes in 200 BCE. This prime meridian was used to provide measurement of the earth, but had many problems because of the lack of latitude measurement. Many years later around the 19th century there were still concerns of the prime meridian. Mu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
180th Meridian
The 180th meridian or antimeridian is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west. On Earth, these two meridians form a great circle that divides the earth into the Western and Eastern Hemispheres. The antimeridian mostly passes through the open waters of the Pacific Ocean, but also across land in Russia, Fiji, and Antarctica. An important function of this meridian is its use as the basis for the International Date Line, which snakes around national borders to maintain date consistency within the territories of Russia, the United States, Kiribati, Fiji and New Zealand. Starting at the North Pole of the Earth and heading south to the South Pole, the 180th meridian passes through: The meridian also passes between (but not particularly close to): *through the Aleutian Island chain of US territory *the Gilbert Islands and the Phoenix Islands of Kiriba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very Long Baseline Interferometry
Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes. Data received at each antenna in the array include arrival times from a local atomic clock, such as a hydrogen maser. At a later time, the data are correlated with data from other antennas that recorded the same radio signal, to produce the resulting image. The resolution achievable using interferometry is proportional to the observing frequency. The VLBI technique enables the distance betwee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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