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Epoch J2000.0 is a standard point in time used as a reference in astronomy. It is precisely defined, as noon, January 1, 2000 Terrestrial Time (TT), which was roughly 11:58:55.816 AM, January 1, 2000 UTC (and GMT). Expressed as a TT Julian date, it is exactly 2451545.0. It was adopted to be used as a basis for cited positions of astronomical objects, to replace the previously-used epoch B1950.0. It can be cited with the coordinates of an object to signify that the object was at that position at that precise time. This allows identification of an object by position, despite movement, such as a star's proper motion. Knowing the motion, a position cited as "epoch J2000.0" can be extrapolated to its current position, and vice versa. Recorded positions at different such epochs allow proper motion of stars to be determined. Citing equatorial coordinates with a J prefix (e.g., "J162702.56+432833.9", which for the purposes of this website, I've termed a J designator) indicates both epoch J2000.0 and J2000.0 equinox, the latter specifying the positioning of the coordinate scales.