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More specifically, the ICRF is an inertial barycentric reference frame whose axes are defined by the measured positions of extragalactic sources (mainly quasars) observed using very-long-baseline interferometry while the Gaia-CRF is an inertial barycentric reference frame defined by optically measured positions of extragalactic sources by the ...
J2000: One commonly used ECI frame is defined with the Earth's Mean Equator and Mean Equinox (MEME) at 12:00 Terrestrial Time on 1 January 2000. It can be referred to as J2K, J2000 or EME2000. The x-axis is aligned with the mean vernal equinox.
The Geocentric Celestial Reference Frame (GCRF) is the geocentric equivalent of the International Celestial Reference Frame (ICRF). Its primary direction is the equinox of J2000.0, and does not move with precession and nutation, but it is otherwise equivalent to the above systems.
The method of modeling the asteroids' perturbations was improved, although the same number of asteroids were modeled. The ephemeris was more accurately oriented onto the ICRF. DE405 covered 1600 to 2200 to full precision. This ephemeris was utilized in the Astronomical Almanac from 2003 until 2014. DE406 was released with DE405 in 1998. A Long ...
The Hipparcos Celestial Reference Frame (HCRF) was similar to ICRF, but earlier, used in association with the Hipparcos satellite, which functioned between 1989 and 1993. That satellite took copious stellar parallax measurements at accuracies exceeding anything otherwise available at the time, thus producing a catalog of stars still in wide use ...
This means that the Earth's rotational North pole does not point quite at the J2000 celestial pole at the epoch J2000.0; the true pole of epoch nutates away from the mean one. The same differences pertain to the equinox. [9] The "J" in the prefix indicates that it is a Julian equinox or epoch rather than a Besselian equinox or epoch.
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GNSS systems: [2] Galileo Terrestrial Reference Frame (GTRF), ITRF2005; own implementation using IGS sites.; GPS just uses WGS 84, ITRF2020 since January 2024 (but used many versions of WGS 84 before), a little modified with International GNSS Service (IGS) implementation, IGS20.