100 Days Until Totality Blog Series: 81 Days Left – Why Do Lunar Eclipses Happen More Often than Total Solar Eclipses in the Same Location?

You have probably seen multiple lunar eclipses in your life, so they seem to be a fairly common occurrence. Conversely, many people have never seen a solar eclipse, which makes them seem more rare. In reality, solar eclipses occur (on average) more than lunar eclipses. The maximum number of solar eclipses in a year is 5, while the maximum amount of lunar eclipses is 3. The reason that locations have more lunar eclipses than solar eclipses is simply due to the differences in the sizes of the shadows. The umbra (darkest region of shadow) cast by the Earth during a lunar eclipse is on average about 5600 miles wide at the Moon’s distance! This huge shadow is larger than the Moon, which allows the entire night side of the Earth to see a lunar eclipse. Comparatively, the Moon’s umbra that it casts is about 80 miles wide, which is obviously very small compared to the size of the Earth. So your odds of seeing a lunar eclipse are much higher for any given area since, half of the planet sees them whenever they occur.

Click on the small image below to see the Earth-Moon system to scale. This can really give you a sense of why these shadows are sized the way they are.

Credit: CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=548718

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