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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 ], 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 ]. | ||
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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. 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 sidereal 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. | ||
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''See also'': | ||
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Revision as of 01:29, 15 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.
See also:
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