This is an old revision of this page, as edited by Urhixidur (talk | contribs) at 11:55, 7 September 2004 (Added time/angle units). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 11:55, 7 September 2004 by Urhixidur (talk | contribs) (Added time/angle units)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)
Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination. RA is comparable to longitude, measured from a zero point known as the vernal equinox point. RA is measured in hours, minutes, and seconds. Being closely tied with sidereal time, it is both a unit of time and of angle. An hour of right ascension is equal to 15 degrees of arc, a minute of right ascension equal to 15 minutes of arc, and a second of right ascension equal to 15 seconds of arc.
RA can be used to determine a star's location and to determine how long it will take for a star to reach a certain point in the sky. For example, if a star with RA = 01:30:00 is at your meridian, then a star with RA = 20:00:00 will be in the meridian 18.5 sidereal hours later.
See also: declination
Category: