Autumnal Equinox Lesson for Kids: Definition & Explanation

Instructor: Kelley Lipke

Kelley has been teaching middle school for six years and has a master's degree in educational administration.

This lesson will introduce you to the astronomical phenomenon known as the autumnal equinox. Learn about what an equinox is, why it occurs, and how it affects people around the world.

The First Day of Fall

Crisp leaves, apple picking, hayrides, and pumpkin patches are all signs that indicate a change of seasons. The long hot days of summer start to dwindle, and the cooler, crisp air of fall begins to settle in. Although we can usually tell by the change in temperatures and the fun festivals coming into town, do we really know exactly when fall begins?

The start of fall is actually marked by an astronomical event known as the autumnal equinox.

Keep reading to find out more about this fascinating phenomenon!

What is an Equinox?

In Latin, the word equinox means 'equal light.' There are two days a year when equinoxes occur---one in September and one in March. On these two days, there is an equal amount of daylight and nighttime, each occurring for twelve hours.

So, why does an equinox occur?

Well, an equinox is the exact moment the sun crosses the celestial equator, which is an imaginary line in the sky that matches up with the equator (which is also an imaginary line that divides the Earth into the Northern and Southern hemispheres).

Most of the year, Earth's axis is tilted, which influences the seasons. It spends about half the year tilted more towards the sun and the other half tiled away from the sun. This is what we know as summer and winter.

However, on the two days a year in which an equinox occurs, Earth is neither tilting toward nor away from the sun, creating a balance between day and night.

The orbit of Earth during an autumnal equinox

When Does the Autumnal Equinox Occur?

The autumnal equinox occurs in September---usually the 22nd or 23rd of the month---and is the official start of fall. The exact time this equinox occurs varies due to time zone differences throughout the world.

In fact, the Northern hemisphere refers to the autumnal equinox as the start of fall, but in the Southern hemisphere, this is actually their spring equinox and it marks the beginning of spring instead. Due to Earth's tilt, the two hemispheres are actually reversed and experience seasons at opposite times of the year.

Northern Lights

Have you ever seen the beautiful display of colorful lights in the night sky? The aurora borealis (or northern lights) is a natural event that occurs in areas of high latitudes, such as Alaska and Canada.

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