RACHEL MARTIN, HOST:
So do you have your solar glasses yet? Maybe you're already on your way to a total eclipse destination. Or maybe, like those of us in Washington, D.C., you'll have to just look for weird shadows and try not to burn out your corneas. Either way, in just five days, across a broad stretch of the United States, the moon will appear to perfectly cover up the glowing disk that is the sun. A total solar eclipse is a rare occurrence. But NPR's Nell Greenfieldboyce reports that it is a celestial stroke of luck that it can happen at all.
NELL GREENFIELDBOYCE, BYLINE: Earth is lucky to have total solar eclipses. Mercury and Venus don't even have moons. Mars has a couple, but they're too small to cover up the sun. Gas giants like Jupiter do have big moons, but it's not like these planets have a solid surface where you can stand and watch an eclipse. Here on our planet, it all comes down to cosmic coincidence.
AMBER PORTER: 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.
GREENFIELDBOYCE: Amber Porter is an astronomer at Clemson University, which is in the path of the upcoming eclipse. From the Earth the moon and the sun seem to take up about the same amount of space in the sky.
PORTER: They appear to be the same size because of their distance away from us.
GREENFIELDBOYCE: And here's another way we're lucky. It's just chance that humans exist at a time when we get to see this perfect alignment, which reveals the eerie, glowing crown of light around our sun. In the past, Earth's eclipses did not look like this. Matija Cuk is a planetary scientist at the SETI Institute.
MATIJA CUK: The size of the sun hasn't really changed over the age of Earth, but the moon has been moving away from Earth over eons. So in the past, it looked bigger.
GREENFIELDBOYCE: The moon is still moving away from Earth. He says every year, it shifts outward about an inch and a half.
CUK: So actually, for billions of years, you can have a total eclipse. But this very evenly matched eclipse, where it's barely total, that happens for a relatively short amount of time.
GREENFIELDBOYCE: In only about 600 million years, the moon will look small enough that it no longer completely covers the sun. That means no more total solar eclipses, so get it while you can. Nell Greenfieldboyce, NPR News.
(SOUNDBITE OF SONG, "BLUE MOON")
THE MARCELS: (Singing) Blue moon, you saw me standing alone without a dream in my heart...
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.