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Why Don’t We Have Eclipses Every Month?

silhouette of woman looking at lunar eclipse
AstroStar/Shutterstock

Part of what makes an eclipse so impressive is its rarity. An eclipse feels like a special occasion. Yet, we know that the solar system operates on a schedule, and the moon, in particular, follows a monthly cycle. So, why don’t we experience regular eclipses?

In ancient China, a solar eclipse was taken as a warning to the emperor. After an eclipse, the emperor would eat a vegetarian diet, organize rituals to get the sun back, and avoid the palace until the perceived danger had passed.

Today, we take eclipses far less seriously. Still, it’s hard to deny that they are an impressive sight. When the sun or moon gets partially (or fully) blacked out, who can avoid stopping and watching in wonder for a few minutes?

What Are Eclipses?

To move closer to our answer, let’s take a look at what eclipses really are.

Ancient cultures explained the darkening of the sun and moon with all kinds of superstitions and supernatural elements. However, today’s modern science can give us the details on what’s actually happening in the sky.

Solar and Lunar Eclipse Comparison Infographic
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A solar eclipse—when the sun’s light is blocked—happens when the moon gets between the Earth and the sun, casting a shadow on the Earth. A lunar eclipse—when the moon’s light is blocked—happens when the Earth gets between the moon and the sun, casting a shadow on the moon.

Why We Don’t Get Eclipses More Often

Knowing this, and knowing that the moon orbits the Earth in a little under a month, it seems like we should have eclipses far more often. Presumably, the moon, sun, and Earth would all line up about twice a month as the moon makes its orbit. However, the truth is a little more complicated.

Eclipses require all three celestial bodies to line up perfectly. Most of the time, though, they don’t due to the moon’s orbit. As the moon orbits the Earth, it follows a tilted path rather than a flat one. The Earth and the moon don’t orbit on the same plane, so their shadows rarely line up for an eclipse.

Have you ever noticed that lunar and solar eclipses often happen close together? That’s because the sun, moon, and Earth have lined up for the first time in a long time, and both kinds of eclipses become possible for a while. But soon, the moon follows its tilted path out of alignment with the rest.

If we had monthly eclipses, they probably wouldn’t feel like anything special. But instead, we have rare eclipses to get excited about. And, to make them even more exciting, you can only see solar eclipses from certain parts of the world, because the moon’s shadow doesn’t cover the whole Earth.

So, next time there’s an eclipse, take a moment to watch the spectacle. It may not be a serious omen like ancient cultures believed, but it’s certainly something you don’t see every day.

Elyse Hauser Elyse Hauser
Elyse Hauser is a Seattle-based writer and editor with a Master's in Writing Studies from Saint Joseph's University. Her work has appeared in publications like Racked, Vine Leaves Literary Journal, and Rum Punch Press. She was awarded a 2017 Writing Between the Vines residency.  Read Full Bio »