This year the Autumnal Equinox falls on Friday, September 22, 2017. That's also the day that Autumn begins.
Equinox" literally means "equal night", giving the impression that the night and day on the equinox are exactly the same length; 12 hours each. But is it?
Sure the name suggests it and it is widely accepted, but is it really true that day and night are exactly equal on the equinox? Close, but not quite!
Our Earth spins around its own axis approximately every 24 hours (a sidereal day is 23 hours, 56 minutes, 4 seconds).
Earth's orbit takes 365 days, 5 hours, 48 minutes and 45 seconds (365.242189 days). We call that a year.
Planet Earth is actually tilted at an angle of around 23.4 degrees toward the celestial pole, which is a certain point in the sky. As Earth makes its yearly orbit, 1 hemisphere faces the sun more than the other, the side that has Summer.
The equinoxes marks the exact moment twice a year when the Earth's axis is not tilted toward or away from the Sun at all.
Even if day and night aren’t exactly equal on the day of the equinox, there are days when day and night are both very close to 12 hours. However, this date depends on the latitude, and can vary by as much as several weeks from place to place.
So the next time you hear that day and night are exactly the same on equinox, you'll know better.
Kahl Consultants wishes a happy Fall to all - except for our readers in the southern hemisphere, here's wishing you a happy Spring!