What happens during an equinox?
During an equinox, the sun is directly above the Earth's equator, and the length of day and night is approximately equal worldwide. The word "equinox" is derived from Latin, meaning "equal night." There are two equinoxes each year: the vernal (spring) equinox, which occurs around March 20th, and the autumnal (fall) equinox, which occurs around September 22nd.
During an equinox, the tilt of the Earth's axis is perpendicular to the sun's rays, causing the sun to shine directly on the Earth's equator. This causes the sun to appear directly overhead at noon along the equator, resulting in equal lengths of day and night around the world.
The equinoxes mark the beginning of spring and autumn in the Northern Hemisphere. In the vernal equinox, the Northern Hemisphere transitions from winter to spring, while in the autumnal equinox, it transitions from summer to fall. In the Southern Hemisphere, the seasons are reversed.
Notably, during an equinox, the sun rises due east and sets due west, and the length of daylight gradually lengthens (vernal equinox) or shortens (autumnal equinox) as the Earth progresses in its orbit around the sun.