The position of an object on the celestial sphere, as seen from the Sun, referred to the mean equator and equinox at the beginning of the year; it is thus the apparent place corrected for annual parallax, proper motion, precession, aberration, and nutation. All observations of the apparent place of a star made during a particular year may be reduced to the mean place for the beginning of that year, so that they can be intercompared; in practice, though, all observations made over a period of several years are reduced to a common epoch, e.g. J2000.0.
Related category• CELESTIAL MECHANICS
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