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Earth-centered inertial (ECI) coordinate frames have their origins at the center of mass of Earth and are fixed with respect to the stars. [1] " I" in "ECI" stands for inertial (i.e. "not accelerating "), in contrast to the "Earth-centered – Earth-fixed" ( ECEF ) frames, which remains fixed with respect to Earth's surface in its rotation ...
When the mean equator and equinox of J2000 are used to define a celestial reference frame, that frame may also be denoted J2000 coordinates or simply J2000. This is different from the International Celestial Reference System (ICRS): the mean equator and equinox at J2000.0 are distinct from and of lower precision than ICRS, but agree with ICRS ...
The ECI reference frame is not truly inertial because of the slow, 26,000 year precession of Earth's axis, so the reference frames defined by Earth's orientation at a standard astronomical epoch such as B1950 or J2000 are also commonly used. [2]: 24
A reference frame has been defined as "a catalogue of the adopted coordinates of a set of reference objects that serves to define, or realize, a particular coordinate frame". [7] A reference system is a broader concept, encompassing "the totality of procedures, models and constants that are required for the use of one or more reference frames ...
BeiDou Coordinate System, China Terrestrial Reference Frame (CTRF) 2000 = ITRF97 at epoch 2000.0; own implementation. GLONASS PZ-90.11 is nominally its own system, but is quite close to ITRF and uses many of the same techniques. [2] National systems: United States: WGS 84 (see above); domestic use is mainly based on NAD 83 instead.
But the argument of perihelion, longitude of the ascending node and the inclination are all coordinate-dependent, and are specified relative to the reference frame of the equinox and ecliptic of another date "2000.0", otherwise known as J2000, i.e. January 1.5, 2000 (12h on January 1) or JD 2451545.0. [4]
An observational frame (such as an inertial frame or non-inertial frame of reference) is a physical concept related to state of motion. A coordinate system is a mathematical concept, amounting to a choice of language used to describe observations. [3]
The Pontiac Sunbird (also known as the Pontiac J2000 and Pontiac 2000) is a model line that was manufactured and marketed by Pontiac from the 1976 to the 1994 model years. . Loosely deriving its name from the Pontiac Firebird, the Sunbird was introduced as the eventual replacement for the Pontiac Astre, replacing it entirely in 1978 as the smallest Pontiac (the later T1000 was slotted below it ...