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First Point of Aries

The First Point of Aries, also called the vernal equinox point, is one of the two points on the celestial sphere where the celestial equator intersects the ecliptic. It is defined as the position of the Sun on the celestial sphere at the time of the vernal equinox. It was named after the constellation in which it occurred in ancient times - Aries. However due to precession, the point gradually moves around the ecliptic. It entered the constellation Pisces in about 70 BC and will enter Aquarius in about 2600. The other such point, at the autumnal equinox, is the First Point of Libra.

In the equatorial coordinate system the First Point of Aries is defined to have a right ascension of zero. The declination is also zero due to the position on the celestial equator.