[♪ INTRO] As one of the most impressive astronomical events we can witness from Earth, a total solar eclipse is a jaw-dropping reminder that our planet is part of an elaborate celestial dance.

But because that dance shifts ever so slightly over time, total solar eclipses won’t last forever. So it is natural to wonder: When will we see the last one?

We experience total solar eclipses whenever the Earth, the Moon, and the Sun line up so precisely that the Moon completely blocks our view of the Sun. Because the Moon’s orbit around the Earth and the Earth’s orbit around the Sun aren’t perfectly level with one another, that precise alignment happens every 18 months or so. Now, it goes without saying that our Moon is much, much smaller than the Sun, but it’s also much, much closer, so it appears almost exactly the same size.

If that sounds like a coincidence to you, you’re right. It’s a complete coincidence. And it’s a fleeting one.

Thanks to gravitational interactions between the Earth and the Moon, our natural satellite is actually moving away from us at a rate of about 3.8 centimeters per year. This is something we’ve been measuring since Apollo astronauts installed mirrors on the lunar surface that scientists can bounce lasers off to measure how long the signal takes to get there and back. If you want to know more about why the moon is moving away, you can check out our great video on Lunar Recession.

Ultimately though, this recession means that, eventually, the Moon will appear too small in the sky to completely block the Sun’s surface. No more total solar eclipses. According to some back-of-the-envelope math, that’ll happen when the Moon’s orbit is about 23,000 kilometers wider than it is now.

So at the current recession rate of 3.8 centimeters per year, we’ll get to enjoy total solar eclipses for another 600 million years or so. Which means it’s going to take me at least 599 million years to start planning the goodbye party. But in reality, the math is a little more complicated than that.

It’s likely the recession rate has varied throughout the Moon’s history, and will vary in the future. This is due to things that slightly shift the gravitational interactions our planet has with our moon, like plate tectonics, climate events, and the movement of rock inside the Earth’s core and mantle. With that extra detail, scientists expect total solar eclipses to start being much more irregular and infrequent about 620 million years from now, with the very last happening in around 1.2 billion years.

That feels like forever compared to how long our species has been wandering the world. So there will be plenty of opportunities for humanity to keep on witnessing this amazing phenomenon. If any of us are still around by then, not having total solar eclipses might be the least of the bummers astronomy will be throwing our way.

As our Sun ages, it’s going to get brighter. A billion years from now, it’ll be so bright, Earth’s surface will be too hot for any life to thrive there. So while the days of an Earth-based total solar eclipse are numbered, so are ours.

There’s a good chance there’ll be no one left to watch the very last one. But hey, that gorgeous coincidence had a pretty good run. Thanks for watching this episode of SciShow.

If you’d like to learn more about lunar eclipses plus some awesome science that humans can do with them…we’ve got you covered. Check out our video about new and ancient lessons from lunar eclipses. [♪ OUTRO]