Equinox facts for kids

How the Sun lights the Earth on the day of equinox

An equinox is a special time when the sun shines directly over the equator. This happens twice every year. The word equinox comes from two Latin words that mean "equal" and "night."

Around the time of an equinox, the daytime and nighttime hours are almost the same length all over the Earth. This is because the Sun's light spreads equally across both the northern and southern parts of our planet.

The exact day and time of an equinox can be slightly different depending on where you are. Generally, they happen around March 20 and September 22. These days often mark the start of spring and autumn (or fall in the US).

Many cultures have celebrated these times with festivals because it was easy to notice the equal day and night.

What Happens During an Equinox?

During an equinox, the line that separates day from night on Earth (called the "solar terminator") stands straight up, going from the North Pole to the South Pole. This means both the northern and southern parts of Earth get the same amount of sunlight.

Imagine the Sun being directly overhead for someone standing on the equator. That's what happens during an equinox! The Sun appears to cross the equator, moving north in March and south in September.

Equinoxes are very important for understanding the seasons. In the northern half of the world, the March equinox signals the start of spring. The September equinox marks the beginning of autumn. Some cultures, like those following the Iranian calendars, even celebrate the March equinox as their New Year, called Nowruz.

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  How the Earth is lit by the Sun during the March equinox.

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  The Earth's path around the Sun makes the Sun appear to move along the red line (ecliptic) in the sky.

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  A diagram showing Earth's seasons from the north.

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  A diagram showing Earth's seasons from the south.

When Do Equinoxes Happen?

The dates of the equinoxes can shift slightly each year. This is because our calendar, the Gregorian calendar, isn't perfectly matched with Earth's orbit around the Sun.

Long ago, when Julius Caesar created the Julian calendar in 45 BC, he set March 25 as the spring equinox. But over many years, the calendar slowly drifted. By the year 300 AD, the spring equinox was around March 21.

Later, in the 1500s, Pope Gregory XIII created the modern Gregorian calendar to fix this drift. He wanted the spring equinox to be on March 21 again, which was important for setting the date of Easter. This new calendar helped keep the equinoxes closer to their traditional dates.

Different Names for Equinoxes

You might hear equinoxes called by different names:

• Vernal equinox and autumnal equinox: These are older names. "Vernal" means spring, and "autumnal" means autumn. However, these names can be confusing because when it's spring in the northern half of the world, it's autumn in the southern half!
• March equinox and September equinox: These names are simpler because they just refer to the month they happen in. This avoids confusion about seasons in different parts of the world.
• Northward equinox and southward equinox: These names describe the direction the Sun appears to be moving. The northward equinox (in March) is when the Sun crosses the equator moving north. The southward equinox (in September) is when the Sun crosses the equator moving south. These terms are also useful for talking about other planets!

Related pages

• Solstice

Images for kids

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  Earth at the March 2019 equinox.

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  When Saturn is at equinox its rings reflect little sunlight, as seen in this image by Cassini in 2009.

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  Day arc at 0° latitude (equator) At the equator, the Sun passes directly overhead at noon, so a straight object like a pole would have no shadow.

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  Day arc at 20° latitude The Sun reaches high in the sky, and its path at sunrise and sunset is quite steep.

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  Day arc at 50° latitude The time when the sky is still light before sunrise or after sunset (twilight) lasts almost two hours.

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  Day arc at 70° latitude The Sun doesn't get very high in the sky, and its path is at a shallow angle. Twilight lasts for more than four hours.

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  Day arc at 90° latitude (pole) At the poles, the Sun would appear to stay right on the horizon all day long, if not for the atmosphere bending its light.

See also

In Spanish: Equinoccio para niños