Are Day and Night Each Exactly 12 Hours Long on the Spring Equinox?

It is a common misconception that the day and night are each exactly 12 hours long on the spring equinox — the day when the center of the sun crosses over the Earth's equator, which is typically about 20 March. On the spring equinox, also known as the vernal equinox, there is slightly more daylight than darkness. It is actually two to three days before the equinox when the days are nearly equal parts day and night. For example, three days before the equinox, there is about one more minute of darkness, but on the day of the event itself, there might be about eight more minutes of daylight.

More about the spring equinox:

  • The spring equinox and the fall equinox, or autumnal equinox, are the only days of the year when the sun rises from due east and sets at due west.
  • Before 1582, the design of the commonly used Julian calendar caused the spring equinox to fall one day earlier every 128 years — which eventually would have made it happen during the winter. Pope Gregory XIII altered the calendar slightly in 1582 to prevent this occurrence, which is why the commonly used calendar is now known as the Gregorian calendar.
  • The vernal equinox begins six months of uninterrupted daylight for the North Pole and six months of darkness for the South Pole.
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