Equinox (celestial coordinates): Difference between revisions

bibcode = 1997A&A...323L..49P
m (CS1 maint: Explicit use of et al. -> display-authors/editors=etal using AWB)
(bibcode = 1997A&A...323L..49P)
* [[Constellation]] boundaries were defined in 1930 along lines of [[right ascension]] and [[declination]] for the B1875.0 epoch.
* Occasionally, non-standard equinoxes have been used, such as B1925.0 and B1970.0
* The [[Hipparcos Catalog]] uses the [[International Celestial Reference System|ICRS]] coordinate system (which is essentially equinox J2000.0) but uses an epoch of J1991.25. For objects with a significant [[proper motion]] assuming that the epoch is J2000.0 leads to a large position error. Assuming that the equinox is J1991.25 leads to a large error for nearly all objects.<ref>{{cite journal | urlbibcode =http://adsabs.harvard.edu/cgi-bin/bib_query? 1997A&A...323L..49P | author=Perryman, M.A.C. | display-authors=etal | title=The Hipparcos Catalogue | journal= Astronomy &amp; Astrophysics | volume=323| pages=L49-L52|year=1997}}</ref>
 
Epochs and equinoxes for orbital elements are usually given in [[Terrestrial Time]], in several different formats, including: