At exactly  2:46 p.m.  on March 20, the Sun will cross an invisible line in the sky, and the entire planet will feel the shift.

This is the March equinox, the moment the Sun passes directly over Earth’s equator on its journey northward. For the Northern Hemisphere, it marks the beginning of spring. For the Southern Hemisphere, autumn begins. Everywhere on Earth, the Sun rises almost exactly due east and sets almost exactly due west, and day and night are nearly equal in length.