There are plenty of articles and essays out there explaining why witnessing an eclipse totality is worth any effort, how profound and even transformational the experience can be. But there’s one aspect that receives almost no attention: the amazing cosmic luck that total solar eclipses happen at all.

Consider this: our moon happens to be just the right size, at just the distance between us and our sun, in just the right space as the moon orbits us and we orbit the sun, to perfectly cover the face of the sun. It reveals, for us, the glorious plasma jets of the sun’s corona.

Since seeing the 2017 eclipse in person, I’ve been wondering, just how lucky are we to get this perfect alignment? And a couple of days ago, astrophysicist Grant Tremblay confirmed it to me.

“It is really an incredible cosmic coincidence,” he told me on All Things Considered Friday. “And I promise you, it really is just a coincidence, but it's a profoundly lucky one.”

To get a sense of just how lucky, I asked him to break down the numbers.

“Is the sun and the moon the same size? Obviously not!” he said. “We know from pure geometry that things that are further away from you have a smaller, so-called ‘angular size’ in the sky than things that are closer to you. The sun is 400 times larger in diameter than the moon is.”

The sun is — roughly — 865,000 miles across to the moon’s 2,160 miles.


“The moon is, from the Earth, roughly about 239,000 miles away,” Tremblay explained. “The sun is absolutely enormous — it’s 865,000 miles in diameter — but it's also 400 times further away from the moon. The sun is 93 million miles away.”

And herein lies what Tremblay calls the “cosmic coincidence.”

“Because the sun is 400 times larger than the moon is but also basically 400 times further away, they are almost exactly the same size in the sky,” he said. “When you get these chance alignments, the disk of the moon totally blocks out the bright disk of the sun.”

For me, the coincidence is downright miraculous when you factor in the fact that our planet also happens to be the perfect place for an eclipse party: in the habitable “Goldilocks zone,” just the right distance from our star, with just the right gravity and mix of elements to develop life that would ultimately evolve sentience — and be able to appreciate the incredible eclipse show on their incredible little planet.

As I told Tremblay, I’m not a creationist, but it made me wonder: is it all somehow more than just a coincidence?

He laughed and said, “It is really lucky.”