For longitude, the zero point is the Prime Meridian on the geographic equator; for right ascension, the zero point is known as the first point of Aries, which is the place in the sky where the Sun crosses the celestial equator at the March equinox.
The zero point is the Prime Meridian on the geographic equator. This is for longitude. The zero point is known as the first point of Aries. This was for right ascension. The first point of Aries is the place in the sky where the Sun crosses the celestial equator at the March equinox.