At a Glance

Total solar eclipses will no longer be possible in 600 million years, scientists say.This is because the moon is slowly creeping away from the Earth and won't remain the ideal distance to block out the sun.

Trips have been planned and special glasses purchased for next Monday's Great American Solar Eclipse. But did you know total solar eclipses haven't always been possible, and generations far into the future will never have that experience either?

These days, the sun's distance from the Earth combines perfectlywith the differences in the size of the sun and Earth's moon , according to NPR. Because of this perfect alignment, we get to watch the moon completely block out the sun, save for its stunning but creepy corona, the report added.

"They appear to be the same size because of their distance away from us,"Amber Porter, an astronomer at Clemson University, told NPR. "Even though the moon is about 400 times smaller than the sun, it's about 400 times closer to us here on Earth, which is how that perfect kind of magic happens."

(MORE: )

Here's why total solar eclipses won't be around forever: The moon is moving away from the Earth at a rate of an inch and a half every year. This is because the moon's gravity is slowing the Earth's rotation by 2.3 milliseconds each century, and energy lost by our planet is being absorbed by the moon, , according to Space.com.

In fact, when the moon was formed, scientists believe it was 14,000 miles away from the Earth. Four and a half billion years later, the satellite is now 250,000 miles away, and that distance increases each year.

Despite the growing distance, total solar eclipses are still expected to be around for a while, but in 600 million years, the moon will be so far from Earth that it'll no longer cover the sun completely and future eclipses will only be partial, NPR said.