Every six months, once in March and again in September, an equinox splits Earth’s day almost in half, giving us about 12 hours of daylight and 12 of night.

On March 20, 2023, the vernal equinox will signal the coming of spring for the Northern Hemisphere. Then, on September 23, nature will once again bring us the autumnal equinox, the time of year that ushers in fall in the North. Those dates are swapped for the vernal and autumnal equinoxes in the Southern Hemisphere. (Here's why each season begins twice.)

Our planet normally orbits the sun on an axis that’s tilted 23.5 degrees, meaning that the hemispheres trade off getting more warmth from the sun. Two times a