The next total solar eclipse is 500 million miles away

This past week, there was a total solar eclipse, visible from a path stretching along far northern Russia, Greenland, Iceland, and Spain. Like many of this year’s eclipse chasers, I was clouded out – though I did have a lovely couple minutes of darkness on an Icelandic fjord. I’m already planning for the next time the Moon blocks the Sun: in the Mediterranean a bit less than a year from now. But most people don’t know there’s another total eclipse even sooner – and I can guarantee you there won’t be a cloud in the sky.

My cloudy totality

The Moon is about 400x smaller than the Sun, and also about 400x closer to Earth. That means it just barely blocks the Sun in Earth’s skies, revealing the Solar corona – the Sun’s ghostly outer atmosphere. The Moon’s distance to the Earth and the Earth’s distance to the Sun change slightly over the course of their orbits, so the apparent size of the Moon relative to the Sun (called the “magnitude” of the eclipse) ranges from a little under 0.91x to a bit over 1.08x. When the magnitude is less than 1, we get an “annular” eclipse where the Sun looks like a ring of fire. Over 1, we get a total eclipse.

Total eclipse of August 12, 2026 from Spain

Annular eclipse of October 14, 2023 from Texas

No other planet in our solar system has a round moon that’s the right size and distance to have such perfect eclipses. Jupiter’s moon Callisto is the closest, with a minimum magnitude of about 1.35. Minute Physics made a video on this a while back, if you want to see more.

But why limit ourselves to just the planets? The outer planets have several moons each, and one round moon can cast a shadow on another one, giving it an eclipse. So can we get a solar eclipse by one round moon viewed from another that’s as good as the eclipses on Earth?

I set out to tackle this question a few years ago with – what else – a giant spreadsheet. I grabbed the orbital and size information for each moon in the solar system from the internet, and set up a table for how far away you’d have to be to see it perfectly block out the Sun. Then I looked for what other moons could in principle be that distance away.

There’s a lot of variables here. Each of these moons is on its own independent elliptical orbit around its parent planet. That means the distances between them can vary wildly. And their parent planets are also on elliptical orbits around the Sun, so the Sun’s size in the sky can vary a bit, too. Taking all this together, it turns out there’s a few combinations that could produce total eclipses with magnitudes similar to total eclipses on Earth.

So when’s the next one? Conveniently, astronomers already track when one moon of a planet passes into the shadow of another. These events are visible from Earth as a sudden dimming of the more distant moon. It’s part of a broader category of “mutual events” involving multiple moons, which also includes a moon passing behind another as viewed from Earth. Scientists observe mutual events to help refine their models of those moons’ orbits.

A string of mutual events are happening around Jupiter this year and next, and you can find the whole list here. Unfortunately, “magnitude” in the prediction tables is a different quantity than the magnitude we’re looking for. It’s possible calculate that information from data we know, but it doesn’t seem like anyone’s published it yet. So that’s what I’m going to do for the next post! I’ve already tested the system out, and I’ve found that on November 16th, 2026, Io will eclipse the Sun as viewed from Callisto with a magnitude of 1.07. So keep an eye out!