Definition:Equinox
Definition
The equinoxes are the points on the celestial sphere where the ecliptic intersects the celestial equator.
These are the points at which the sun, in its apparent annual motion, crosses the celestial equator.
Vernal Equinox
The vernal equinox is the equinox at which the sun crosses the celestial equator from south to north.
In the northern hemisphere this crossing occurs sometime around $21$ March.
Autumnal Equinox
The autumnal equinox is the equinox at which the sun crosses the celestial equator from north to south.
In the northern hemisphere this crossing occurs sometime around $23$ September.
Also known as
The equinoxes are also known as the equinoctial points.
Also see
- Results about equinoxes can be found here.
Linguistic Note
The word equinox derives from the Latin for equal night, as it is the time of year when the daylight last as long as the night time.
It is pronounced e-qui-nox, where the first e can either be as in egg or as in equal.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): celestial sphere
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): equinoxes (equinoctial points)
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): celestial sphere
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): equinoxes (equinoctial points)