the position on the celestial sphere occupied by the sun on or about March 21 when its path on the ecliptic crosses the celestial equator going from south to north. This point is also called the March equinox and the First Point of Aries.
the point on the ecliptic at which the Sun is in the plane of the Earth's equator and day and night are of equal length all over the Earth. The vernal equinox defines 0° of the sign Aries, or the beginning of the astrological cycle. The vernal equinox is also defined as the line formed by the intersection of the Earth's equatorial and orbital planes, and the direction (vector) on that line towards the Sun when the Sun is passing from below the equatorial plane to above it. (The opposite direction on that line/vector is known as the autumnal equinox.) Because the Earth's pole wobbles in a 26,000-year cycle, so too does the Earth's equatorial plane, and hence the point of intersection of the equatorial and orbital planes. Thus causes the vernal equinox to move (precess) backwards among the stars in a 26,000 year cycle known as the precession of the equinoxes.
The intersection of ecliptic and equator that occurs when the apparent path of the Sun crosses the equator at a northward inoculation. This is the first day of spring in the northern hemisphere, and this point (degree) of the ecliptic is the designated starting point for the signs: 0 degrees Aries.
the point on the celestial sphere at which the plane of Earth's orbit crosses the plane of Earth's equator, moving from south to north. This point defines zero hours right ascension. See Ecliptic Figure.
The moment when the Sun crosses the celestial equator travelling in a northward direction, on or about March 21. In the northern hemisphere, it marks the first day of spring. The term is also applied to the Sun's position in the sky at that moment. It is one of two points where the ecliptic and the celestial equator intersect, the other being the autumnal equinox.
Taking place in the Northern Hemispheric spring, it is the point at which the ecliptic intersects the celestial equator. Days and nights are most nearly equal in duration. It falls on or about March 20 and is considered the beginning of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. It is the astronomical opposite of the autumnal equinox.
Equinoxes are days in which day and night are of equal duration. The two yearly equinoxes occur when the Sun crosses the celestial equator. The vernal (spring) equinox occurs on March 21; the autumnal equinox occurs on September 21.