The sun appears directly over the equator on two specific dates each year:

* March 20/21: This is the vernal equinox, marking the beginning of spring in the Northern Hemisphere and autumn in the Southern Hemisphere.

* September 22/23: This is the autumnal equinox, marking the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.

These dates are approximate as the exact time varies slightly from year to year.