Right ascension: Difference between revisions

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	'''Right ascension''' (RA; symbol α : Greek letter ]) is the ] term for one of the two ]s of a point on the ] when using the ]. The other coordinate is the ]. RA is comparable to longitude, measured from a zero point known as the ''']'''. RA is measured in hours, minutes, and seconds; with ~~one~~ hour equal to 15 ~~degrees~~.		'''Right ascension''' (RA; symbol α: Greek letter ]) is the ] term for one of the two ]s of a point on the ] when using the ]. The other coordinate is the ]. RA is comparable to longitude, measured from a zero point known as the ''']'''. RA is measured in hours, minutes, and seconds. Being closely tied with ], it is both a unit of time and of angle. An '''hour of right ascension''' is equal to 15 ]s of arc, a '''minute of right ascension''' equal to 15 ], and a '''second of right ascension''' equal to 15 ].

	RA can be used to determine a ]'s location and to determine how long it will take for a star to reach a certain point in the ]. For example, if a star with RA = 01:30:00 is at your ], then a star with RA = 20:00:00 will be in the meridian 18.5 ] hours later.		RA can be used to determine a ]'s location and to determine how long it will take for a star to reach a certain point in the ]. For example, if a star with RA = 01:30:00 is at your ], then a star with RA = 20:00:00 will be in the meridian 18.5 sidereal hours later.

	See also: ]		See also: ]

Revision as of 11:55, 7 September 2004

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.