The vernal or spring equinox occurs around 21 March each year, although this is only spring for observers in the Northern Hemisphere. On this day, the Sun crosses from the south to the north of the celestial equator at the ascending node of its orbit, and the length of daylight and night are the same for observers anywhere on the Earth (with minor latitude corrections due to refraction).

The vernal equinox is also known as the First Point of Aries, since about 2,000 years ago, the point on the celestial sphere where the ecliptic and celestial equator crossed was in the constellation Aries. However, due to the precession of the equinoxes, the vernal equinox now occurs in Pisces.