I learned that the eytmology of equinox is equi (equal) nox (night). So I would assume that the sunrise and sunset of our upcoming vernal equinox (March 21) would be at the same time (e.g. 6:05 am and 6:05 pm), which would equal 12 hours of day and night. But the rise and set on March 21 is 6:58 am and 7:10 pm. That’s about 12 hours and 12 minutes. But on March 16 sunrise and sunset was very close to being precisely 12 hours. Why is the equinox on March 21 and not on March 16?
In: Geology
The moment of sunrise and sunset is considered to be when the centre of the sun is 50 minutes of arc (50 sixtieths of a degree) below the horizontal. This is because it’s 16 minutes from the centre of the sun to the edge of the sun and the atmosphere makes things on the horizon appear 34 minutes higher than they really are. This makes the day longer than the night at the equinox.
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