What Is an Equinox?
An equinox is one of the two moments each year when the Sun crosses the celestial equator, occurring around March 20 and around September 22–23. Day and night are then close to equal in length across the world. The March equinox marks the astronomical start of spring in the Northern Hemisphere and of autumn in the Southern Hemisphere.
Not Exactly Equal
Because sunlight bends in the atmosphere and the Sun is a disk rather than a point, daylight is slightly longer than night on the equinox itself.
Related Events
Solstices, halfway between equinoxes, mark the longest and shortest days.
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🔗 Related Terms
More Time & Dates Terms
- 24-Hour Clock (Military Time)
- Business Days
- Calendar Quarter
- Chronological Age
- Coordinated Universal Time (UTC)
- Daylight Saving Time (DST)
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Last updated: September 29, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.