Descriptions

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Descriptions of the Epoch of equator and equinox

Designations on the page Descriptions

ICRF Astrometric coordinates: they are referred to the coordinate reference frame of the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP which is supposed to be very close to the International Celestial Reference Frame (ICRF). If the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP are choosen, no transformation is applied. If the planetary ephemerides DE200/LE200 or VSOP87 are choosen, the satellite absolute coordinates are converted first to the FK5 reference system as described in Standish (1982, Astron. Astrophys. V. 114. P. 297-302) and then to the ICRF using the orientation between the FK5 and the ICRS at J2000.0 as described in Feissel and Mignard (1998, Astron. Astrophys. V. 331. P. L33-L36.).

FK5 Astrometric coordinates: they are supposed to be in the FK5 reference frame. If the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP are choosen, a transformation is applied from ICRF to FK5 using the orientation between the FK5 and the ICRS at J2000.0 as described in Feissel and Mignard (1998, Astron. Astrophys. V. 331. P. L33-L36.). If the planetary ephemerides DE200/LE200 or VSOP87 are choosen, corrections to the FK5 are applied as described in Standish (1982, Astron. Astrophys. V. 114. P. 297-302).

J2000 Astrometric coordinates: they are referred to the reference frame of the choosen planetary ephemeris. No transformation is applied. Thus the planetary ephemerides DE405/LE405, DE406/LE406 and INPOP are supposed to be in the ICRF system. The reference frame of the planetary ephemerides DE200/LE200 and VSOP87 are very close to the FK5 reference frame but some corrections are needed.

Mean of the date (IAU76) The satellite astrometric coordinates are converted first to the FK5 reference system as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the equator and equinox of the date with the precession model adopted by IAU in 1976.

True of the date (IAU76, IAU80) The satellite astrometric coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the true equator and equinox of the date with the precession model adopted by IAU in 1976 and with the nutation IAU 1980 (See Seidelmann, 1982, Celest. Mech., v. 27, p. 79-106).

Apparent (IAU76, IAU80) The satellite apparent coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the true equator and equinox of the date with the precession model adopted by IAU in 1976 and with the nutation IAU 1980. See Seidelmann (1982, Celest. Mech., v. 27, p. 79-106). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.

B1950 Mean equator and equinox of B1950.0 based on FK4. Astrometric coordinates.
Initial astrometric coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account E-term of aberration and depends on the time of observation.

B1900 Mean equator and equinox of B1900.0 . Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of B1900.0 with the Newcomb's precession.

Mean of the date (Newcomb) Mean equator and equinox of the epoch of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the date with the Newcomb's precession.

Year Mean equator and equinox of January 1, Year of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of Jan 1, Year of the date with the Newcomb's precession.

True of the date (Newcomb, IAU1948) True equator and equinox of the epoch of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. The FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the date with the Newcomb's precession. Finally the positions are converted from the mean equator and equinox of the epoch of the date to the true equator and equinox of the epoch of the date with the nutation formulae taken from Astr. Papers (1953. V. 15. Part I., IAU 1948, IAU 1952). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.

Apparent (Newcomb, IAU1948) Apparent coordinates referred to the true equator and equinox of the date. At first any initial astrometric coordinates are converted to the FK5 reference system as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. The FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the epoch of the date with the Newcomb's precession. Finally the positions are converted from the mean equator and equinox of the epoch of the date to the true equator and equinox of the epoch of the date with the nutation formulae taken from Astr. Papers. (1953. V. 15. Part I., IAU 1948, IAU 1952). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.

Designations on the page	Descriptions
ICRF	Astrometric coordinates: they are referred to the coordinate reference frame of the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP which is supposed to be very close to the International Celestial Reference Frame (ICRF). If the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP are choosen, no transformation is applied. If the planetary ephemerides DE200/LE200 or VSOP87 are choosen, the satellite absolute coordinates are converted first to the FK5 reference system as described in Standish (1982, Astron. Astrophys. V. 114. P. 297-302) and then to the ICRF using the orientation between the FK5 and the ICRS at J2000.0 as described in Feissel and Mignard (1998, Astron. Astrophys. V. 331. P. L33-L36.).
FK5	Astrometric coordinates: they are supposed to be in the FK5 reference frame. If the planetary ephemerides DE405/LE405, DE406/LE406 or INPOP are choosen, a transformation is applied from ICRF to FK5 using the orientation between the FK5 and the ICRS at J2000.0 as described in Feissel and Mignard (1998, Astron. Astrophys. V. 331. P. L33-L36.). If the planetary ephemerides DE200/LE200 or VSOP87 are choosen, corrections to the FK5 are applied as described in Standish (1982, Astron. Astrophys. V. 114. P. 297-302).
J2000	Astrometric coordinates: they are referred to the reference frame of the choosen planetary ephemeris. No transformation is applied. Thus the planetary ephemerides DE405/LE405, DE406/LE406 and INPOP are supposed to be in the ICRF system. The reference frame of the planetary ephemerides DE200/LE200 and VSOP87 are very close to the FK5 reference frame but some corrections are needed.
Mean of the date (IAU76)	The satellite astrometric coordinates are converted first to the FK5 reference system as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the equator and equinox of the date with the precession model adopted by IAU in 1976.
True of the date (IAU76, IAU80)	The satellite astrometric coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the true equator and equinox of the date with the precession model adopted by IAU in 1976 and with the nutation IAU 1980 (See Seidelmann, 1982, Celest. Mech., v. 27, p. 79-106).
Apparent (IAU76, IAU80)	The satellite apparent coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these astrometric coordinates are reduced to the true equator and equinox of the date with the precession model adopted by IAU in 1976 and with the nutation IAU 1980. See Seidelmann (1982, Celest. Mech., v. 27, p. 79-106). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.
B1950	Mean equator and equinox of B1950.0 based on FK4. Astrometric coordinates. Initial astrometric coordinates are converted first to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account E-term of aberration and depends on the time of observation.
B1900	Mean equator and equinox of B1900.0 . Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of B1900.0 with the Newcomb's precession.
Mean of the date (Newcomb)	Mean equator and equinox of the epoch of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the date with the Newcomb's precession.
Year	Mean equator and equinox of January 1, Year of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. Finally FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of Jan 1, Year of the date with the Newcomb's precession.
True of the date (Newcomb, IAU1948)	True equator and equinox of the epoch of the date. Astrometric coordinates. At first any initial astrometric coordinates are converted to the FK5 reference frame as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. The FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the date with the Newcomb's precession. Finally the positions are converted from the mean equator and equinox of the epoch of the date to the true equator and equinox of the epoch of the date with the nutation formulae taken from Astr. Papers (1953. V. 15. Part I., IAU 1948, IAU 1952). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.
Apparent (Newcomb, IAU1948)	Apparent coordinates referred to the true equator and equinox of the date. At first any initial astrometric coordinates are converted to the FK5 reference system as described above (see the option "FK5"). Then these coordinates are converted to the epoch B1950.0 FK4-based positions in accordance with the IAU resolutions as described in Aoki et al. (1983, Astron. Astrophys. V. 128. P. 263-267). This conversion takes into account the E-term of aberration and depends on the time of observation. The FK4-based positions of the epoch B1950.0 are converted to the mean equator and equinox of the epoch of the date with the Newcomb's precession. Finally the positions are converted from the mean equator and equinox of the epoch of the date to the true equator and equinox of the epoch of the date with the nutation formulae taken from Astr. Papers. (1953. V. 15. Part I., IAU 1948, IAU 1952). Note that these coordinates are geocentric or topocentric according to the choosen observatory code.