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赤经[Right Ascension] [2005-8-21]
iamet 发表在 ¤〖天文〗
| The azimuthal angle at which the hour circle of a celestial object is located. The rotation axis taken as the direction of the celestial pole. Right ascension is usually measured in units of time (hours, minutes, and seconds), with one hour of time approximately equal to 15° of arc (360°/24 hours=15°/hour). Because the time for the Earth to complete a rotation relative to the "fixed" stars is slightly shorter than the time to complete a rotation relative to the Sun (a sidereal day is 23 h 56 m 4.1 s, whereas a solar day is 24 hours), one hour of right ascension is actually equal to 360°/23.9344...hours= /h. The zero point of right ascension is the first point in Aries, just as the zero point for longitude on the Earth is the prime meridian. |
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