why are days and nights of equal duration throughout the world on 20th march and 22nd september ? Share with your friends Share 1 Santosh answered this On both the dates that you mentioned, the sun is exactly overhead the equator. This make the length of both days and nights almost equal. 3 View Full Answer Ishat Pandit answered this Answer was given few days before. -2 Irene Ann John answered this BECAUSE ON THAT DAYS THE SUN IS OVERHEAD AT THE EQUATOR........ 0