2005/07/28 | 本初子午线[First Point in Aries]
类别(¤〖天文〗) | 评论(0) | 阅读(32) | 发表于 20:15
Also called the zero point of longitude. An arbitrary direction in the reference plane at which right ascension is defined as 0. It is defined as the northern vernal equinox in 1950. Because of precession, the First Point in Aries is actually in the constellation Pisces now!
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