Day, night get equal time Monday as fall begins

Day and night will get equal time for a brief moment Monday as much of the world heads into fall.

The autumnal equinox arrives Monday at 1:19 p.m., marking the start of the fall season for the Northern Hemisphere and the spring in the Southern Hemisphere. On the equator, the sun will be directly overhead at noon. Equinoxes are the only times when both the north and south poles are lit by sunshine at the same time.

In the Northern Hemisphere, sunlight will gradually diminish each day until the winter solstice on Dec. 21.

Equinoxes have been marked and celebrated worldwide for centuries. The fall equinox is often connected with harvest festivals in the Northern Hemisphere. 

But what is the equinox? As the Earth travels around the sun, it does so at an angle.

For most of the year, the Earth’s axis is tilted either toward or away from the sun. That means the sun’s warmth and light fall unequally on the northern and southern halves of the planet.

During the equinox, the Earth’s axis and its orbit align so that both hemispheres get an equal amount of sunlight.

The Northern Hemisphere’s fall — or autumnal — equinox can land between Sept. 21 and 24, depending on the year. Its spring — or vernal — equinox can land between March 19 and 21.

The solstices mark the times during the year when the Earth is at its most extreme tilt toward or away from the sun. This means the hemispheres are getting very different amounts of sunlight — and days and nights are at their most unequal.

During the Northern Hemisphere’s summer solstice, the upper half of the Earth is tilted in toward the sun, creating the longest day and shortest night of the year. This solstice falls between June 20 and 22.

Meanwhile, at the winter solstice, the Northern Hemisphere is leaning away from the sun — leading to the shortest day and longest night of the year. The winter solstice falls between Dec. 20 and 23.