Running in the shadows: Solar eclipses outside Earth

Solar eclipses happen when a moon of a planet partially or completely blocks the Sun. On Earth, solar eclipses only happen on a new moon day (since only then is the sun at the opposite side). The moon’s orbital plane doesn’t exactly align with the orbit of Earth around the sun — had that been the case, there would have been a solar eclipse every new moon. However, that’s not the case — since the moon’s orbit is tilted by around 5 degrees relative to the earth’s solar orbit. Nevertheless, eclipses are not so rare — an average of 4 solar eclipses occur every year!

But what if I said that our planet is not the only one which experiences solar eclipses? How would that look like? Let’s find out!

Mercury and Venus

It is so unfortunate that both of these planets don’t have any moons, and hence cannot witness solar eclipses. At least Venus, sometimes called Earth’s twin, deserved a moon!

Earth

Our beloved home! If you don’t feel special about living here yet, here’s a fact — you cannot witness the magical eclipses as seen on Earth anywhere else in the solar system.

The moon is roughly the same size as the sun — which provides us a unique eclipse among all other planets. When slightly larger than the sun, the moon is able to occult the star completely, yet small enough allow some breathtaking features of the sun to be visible to us. When smaller than the sun, it rather takes a different appearance of a ring. Have a look yourself!

Mars

Mars could have witnessed the same type of eclipses that Earth does, but alas its moons are way too small. Phobos and Deimos are the two moons of Mars. Phobos being the largest (just 22 km in diameter) and the closer moon casts the largest shadow. Deimos on the other hand is a mere 12 km wide, and is way far away than Phobos, appearing as a large dot traversing the sun.

Eclipse of Phobos (left) and Deimos as captured by the Curiosity rover

Jupiter, Saturn, Uranus and Neptune

Here’s the catch with solar eclipses on the gas giants — their moons occult the Sun completely, because of the large distance that makes the Sun appear like a small, bright dot. However, you won’t be able to witness them as these planets don’t have a surface. Oops!

However, we have witnessed how eclipses on Jupiter, Saturn and Uranus appear when seen from space, thanks to the Hubble Space Telescope. Neptune, unfortunately, has no solar eclipses clicked by us. The planet does have solar eclipses in theory, but they are very rare. Take a look at the rest of them!

Io casting a shadow on Jupiter. Although Io is not the largest moon of Jupiter, it casts the largest shadow due to its closer orbit around the planet. Image by the HST.
This image of Saturn was taken by the HST along with four of its moons, two of which are causing an eclipse (left).
Ariel, the fourth largest moon of Uranus, casting a shadow on the planet. Image by HST.

Pluto

Hey, I know, Pluto ain’t a planet anymore. However, the minor planet earns its spot because of one reason — Charon, the largest of Pluto’s five moons, is roughly half the size of the parent planet. This immense size in addition to the fact that the sun is on average 5.9 billion kilometers away leads to the conclusion that the eclipses would be HUGE. They’re also rare though, the last Pluto — Charon eclipse is said to have happened in 1989, continuously for many days. Imagine a 6 hour blackout every day! This is how it might have looked:

Charon casts a shadow almost quarter the size of Pluto

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Rishabh Tatiraju

Rishabh Tatiraju

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Grad student at University of Florida. Computer Science. Astrogeek.