Something absolutely incredible is about to happen this summer, and it is something we won’t see much of in the future for a rather surprising reason. The Great American Solar Eclipse happens on Aug. 21 from coast to coast on the United States, with the band of totality stretching from Oregon to South Carolina and beyond, giving pretty much the entire U.S. a view of at least a partial eclipse.

And although we’re going to get another total eclipse in the United States in 2024, it has been 38 years since the last one, and these events are likely to get rarer still. But why are they so rare? It’s for a few pretty amazing reasons.

The moon follows an elliptical orbit, which presents obstacle No. 1. That means it changes its distance and therefore size relative to Earth, so at some points in its orbit, it’s not big enough to block out the sun. Then there’s the fact that the moon’s orbit is locked into Earth’s equator, meaning that many times we can’t see an eclipse from Earth as the shadow passes above or below Earth.

And even when everything lines up, which does happen two to five times per year, because only a third of thid Earth has land, most eclipses are only visible at sea.

And as the planet’s rotation continues to slow down, resulting in longer days, those total solar eclipses will continue to get more rare. Of course, that’s something that won’t affect us considering what a long time frame that involves.

But it’s still a rare event, and one worth treasuring this August.