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Right ascension (or R.A.) is the angular distance on the celestial sphere measured eastward along the celestial equator from the equinox to the hour circle passing through the celestial object.
Explanatory Supplement to the Astronomical Almanac. 1992. K.P. Seidelmann, Ed., University Science Books, Mill Valley, California.
The list of defined terms to the left is by no means exhaustive with
respect to the general subject of solar system dynamics.
The terms listed are thought to be those more commonly used on our site
and thus appropriate for inclusion on this page.