Equinox Earth Day marks astronomical spring in which hemisphere?

Equinox Earth Day marks astronomical spring in the Northern Hemisphere.

The March equinox occurs when the Sun crosses the celestial equator heading northward. It is called the vernal, or spring, equinox in the Northern Hemisphere, where it marks the astronomical beginning of spring. The same event marks astronomical autumn in the Southern Hemisphere.

An equinox is an exact moment, not an entire day. Around that time, the Sun rises close to due east and sets close to due west, and day and night are approximately equal in length. The date usually falls on March 20, though calendar and time-zone differences can make local dates vary.

A common mix-up is treating “spring” as a worldwide season. Seasons are opposite north and south: March brings spring north of the equator but autumn south of it. Earth Day observances also commonly refer to April 22, so the equinoctial Earth Day and the better-known modern Earth Day date are related but distinct traditions.