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Earth's Orientation Parameters
In geodesy and astrometry, earth orientation parameters (EOP) describe irregularities in the rotation of planet Earth. EOP provide the rotational transform from the International Terrestrial Reference System (ITRS) to the International Celestial Reference System (ICRS), or vice versa, as a function of time. Earth's rotational velocity is not constant over time. Any motion of mass in or on Earth causes a slowdown or speedup of the rotation speed, or a change of rotation axis. Small motions produce changes too small to be measured, but movements of very large mass, like sea currents, tides, or those resulting from earthquakes, can produce discernible changes in the rotation and can change very precise astronomical observations. Global simulations of atmosphere, ocean, and land dynamics are used to create effective angular momentum (EAM) functions that can be used to predict changes in EOP. Components Universal time Universal time (UT1) tracks the Earth's rotation in time, which pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geodesy
Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivalent measurements for other planets (known as '' planetary geodesy''). Geodynamical phenomena, including crustal motion, tides and polar motion, can be studied by designing global and national control networks, applying space geodesy and terrestrial geodetic techniques and relying on datums and coordinate systems. The job title is geodesist or geodetic surveyor. History Definition The word geodesy comes from the Ancient Greek word ''geodaisia'' (literally, "division of Earth"). It is primarily concerned with positioning within the temporally varying gravitational field. Geodesy in the German-speaking world is divided into "higher geodesy" ( or ), which is concerned with measuring Earth on the global scale, and "practical geodes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
GLONASS
GLONASS (russian: ГЛОНАСС, label=none, ; rus, links=no, Глобальная навигационная спутниковая система, r=Global'naya Navigatsionnaya Sputnikovaya Sistema, t=Global Navigation Satellite System) is a Russian satellite navigation system operating as part of a radionavigation-satellite service. It provides an alternative to Global Positioning System (GPS) and is the second navigational system in operation with global coverage and of comparable precision. Satellite navigation devices supporting both GPS and GLONASS have more satellites available, meaning positions can be fixed more quickly and accurately, especially in built-up areas where buildings may obscure the view to some satellites. GLONASS supplementation of GPS systems also improves positioning in high latitudes (north or south). Development of GLONASS began in the Soviet Union in 1976. Beginning on 12 October 1982, numerous rocket launches added satellites to the system, unti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface is made up of the ocean, dwarfing Earth's polar ice, lakes, and rivers. The remaining 29% of Earth's surface is land, consisting of continents and islands. Earth's surface layer is formed of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes the magnetosphere of the Earth, deflecting destructive solar winds. The atmosphere of the Earth consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the energy from the Sun close to the surface. Water vapor is widely present in the atmosphere and forms clouds that cover most of the planet. More solar e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamics Of The Solar System
Dynamics (from Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' "power") or dynamic may refer to: Physics and engineering * Dynamics (mechanics) ** Aerodynamics, the study of the motion of air ** Analytical dynamics, the motion of bodies as induced by external forces ** Brownian dynamics, the occurrence of Langevin dynamics in the motion of particles in solution ** File dynamics, stochastic motion of particles in a channel ** Flight dynamics, the science of aircraft and spacecraft design ** Fluid dynamics or ''hydrodynamics'', the study of fluid flow *** Computational fluid dynamics, a way of studying fluid dynamics using numerical methods ** Fractional dynamics, dynamics with integrations and differentiations of fractional orders ** Molecular dynamics, the study of motion on the molecular level ** Langevin dynamics, a mathematical model for stochastic dynamics ** Orbital dynamics, the study of the motion of rockets and spacecraft ** Quantum c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IERS
The International Earth Rotation and Reference Systems Service (IERS), formerly the International Earth Rotation Service, is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation Parameter (EOP) and International Celestial Reference System (ICRS) groups. History The IERS was established in its present form in 1987 by the International Astronomical Union and the International Union of Geodesy and Geophysics, replacing the earlier International Polar Motion Service (IPMS) and the Earth rotation section of the Bureau International de l'Heure (BIH). The service began operation on January 1, 1988. Since its inception, the IERS has established new bureaus including the GPS Coordinating Centre in 1990, the DORIS Coordinating Centre in 1994 and the GGF Coordinating Centre in 1998. The organization was formerly known as International Earth Rotation Service until 2003 when it formally changed its name to its present form, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nutation
Nutation () is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behaviour of a mechanism. In an appropriate reference frame it can be defined as a change in the second Euler angle. If it is not caused by forces external to the body, it is called ''free nutation'' or '' Euler nutation''. A ''pure nutation'' is a movement of a rotational axis such that the first Euler angle is constant. Therefore it can be seen that the circular red arrow in the diagram indicates the combined effects of precession and nutation, while nutation in the absence of precession would only change the tilt from vertical (second Euler angle). However, in spacecraft dynamics, precession (a change in the first Euler angle) is sometimes referred to as nutation. In a rigid body If a top is set at a tilt on a horizontal surface and spun rapidly, its rotational axis starts precessing about th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Precession
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called ''nutation''. In physics, there are two types of precession: torque-free and torque-induced. In astronomy, ''precession'' refers to any of several slow changes in an astronomical body's rotational or orbital parameters. An important example is the steady change in the orientation of the axis of rotation of the Earth, known as the precession of the equinoxes. Torque-free Torque-free precession implies that no external moment (torque) is applied to the body. In torque-free precession, the angular momentum is a constant, but the angular velocit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Pole
The north and south celestial poles are the two points in the sky where Earth's rotation around a fixed axis, axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day (strictly, per sidereal time, sidereal day). The celestial poles are also the poles of the celestial equatorial coordinate system, meaning they have declinations of +90 degrees and −90 degrees (for the north and south celestial poles, respectively). Despite their apparently fixed positions, the celestial poles in the long term do not actually remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out ci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
West Longitude
Longitude (, ) is a geographic coordinate system, geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another Celestial navigation, celestial body. It is an angular measurement, usually expressed in degree (angle), degrees and denoted by the Greek alphabet, Greek letter lambda (λ). meridian (geography), Meridians are semicircular lines running from geographical pole, pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory, Greenwich, Royal Observatory in Greenwich, England on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west. Because of the Earth's rotation, there is a close connection Time zone, between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 plane o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Celestial Pole
The north and south celestial poles are the two points in the sky where Earth's rotation around a fixed axis, axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day (strictly, per sidereal time, sidereal day). The celestial poles are also the poles of the celestial equatorial coordinate system, meaning they have declinations of +90 degrees and −90 degrees (for the north and south celestial poles, respectively). Despite their apparently fixed positions, the celestial poles in the long term do not actually remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out ci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pole Motion
Polar motion of the Earth is the motion of the Earth's rotational axis relative to its crust. This is measured with respect to a reference frame in which the solid Earth is fixed (a so-called ''Earth-centered, Earth-fixed'' or ECEF reference frame). This variation is a few meters on the surface of the Earth. Analysis Polar motion is defined relative to a conventionally defined reference axis, the CIO (Conventional International Origin), being the pole's average location over the year 1900. It consists of three major components: a free oscillation called Chandler wobble with a period of about 435 days, an annual oscillation, and an irregular drift in the direction of the 80th meridian west, which has lately been less extremely west. Causes The slow drift, about 20 m since 1900, is partly due to motions in the Earth's core and mantle, and partly to the redistribution of water mass as the Greenland ice sheet melts, and to isostatic rebound, i.e. the slow rise of land that was ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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