The Vernal Equinox

 

Sunday, March 20, 2022.  The end of winter.  The beginning of spring.  Days and nights of equal length.  Well, not exactly on that last one.  There is a point in time where the amount of light and dark are the same, but that’s not the equinox, that’s the equilux.  We don’t talk about the equilux.  It doesn’t get any respect.

 

The vernal equinox is when the sun appears overhead directly over the equator, so it would seem that that would make day and night exactly the same length, but that point in time, the equinox, marks when the center of the sun is directly over the equator.  There is more to the sun than just the center, so even when the center of the sun is still below the horizon, the outer edge of the sun is already peeking above it.  Same for sunset.  Even after the center of the sun is below the horizon, the trailing edge of the sun is still visible, so we still have sunlight.  On either equinox, vernal and autumnal, at our latitude, daylight is about eight minutes longer than dark.  There is also a thing about the light of the sun being diffracted through our atmosphere and appearing before it is really actually there, but let’s focus on one thing at a time.