Why Solar Eclipses Don't Happen Every Month (Animation)

A new NASA video explains what determines when Earth experiences solar eclipses — and why they don't happen every month, as the moon crosses between the sun and the Earth.

To prepare for the 2017 total solar eclipse, which will cross the continental United States on Aug. 21, NASA illustrated how the moon orbits the Earth and why the natural satellite's shadow sometimes lines up just right to move across Earth's surface, effectively blotting out the sun for a short period of time.

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Because the moon's orbit wobbles up and down with respect to the Earth, the satellite's shadow can be too high or too low to cause a solar eclipse. If the moon partially covers the sun for a given location, that area experiences a partial solar eclipse. But if the moon fully covers the sun, it will cause either a total solar eclipse or an annular solar eclipse; that's when a bright ring of light is still visible in the sky around the dark silhouette of the moon.

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

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Sarah Lewin
Associate Editor

Sarah Lewin started writing for Space.com in June of 2015 as a Staff Writer and became Associate Editor in 2019 . Her work has been featured by Scientific American, IEEE Spectrum, Quanta Magazine, Wired, The Scientist, Science Friday and WGBH's Inside NOVA. Sarah has an MA from NYU's Science, Health and Environmental Reporting Program and an AB in mathematics from Brown University. When not writing, reading or thinking about space, Sarah enjoys musical theatre and mathematical papercraft. She is currently Assistant News Editor at Scientific American. You can follow her on Twitter @SarahExplains.