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Science Series: Vernal Equinox
Science of the Spring
What is the Vernal Equinox?
In Colorado, we have a saying: we begin the first day of Spring like we began the Fall: with snow. This symmetry is relevant, as the beginning of Spring and Fall coincide with the Equinox.
This word consists of two Latin root words, aequus and nox, meaning “equal night,” referring to the fact that daylight and nighttime are equal in duration.
Equal Day and Night?
Almost. There’s actually more day than night on the day of an Equinox for two reasons. Our atmosphere bends (refracts) sunlight upward. Also, the Sun isn’t a single point of light but a large disk that’s very far away, about 92M miles away. These factors add more daylight to the Equinox. The actual date of sunlight equality is 3 or 4 days ahead of the Equinox. But let’s keep this between us; we don’t want to spoil it for everyone else.
Date of Spring
This year, the vernal equinox (Spring) occurs on March 20 at 09:02 UTC. This means Temps Universel Coordonne, or Coordinated Universal Time if you don’t speak French, roughly equivalent to Greenwich Mean Time if you’re British, or Zulu Time if you’re a pilot. In the U.S., that’s 05:02 PM Eastern Time on March 20.
