On Monday, Aug. 21, it'll get dark during the day. For a few minutes, the moon will orbit perfectly between Earth and the sun and cause a total solar eclipse.
It's been 38 years since this last happened in the continental U.S., and this one will probably create even more of a buzz: Millions of people in 14 states will see the sun blacked out — and that's before we count the millions of others who will travel to see it.
"We don't have a precedent for this, so it's hard to predict," Dr. Angela Speck says.
Speck directs the astronomy department at the University of Missouri. She's been investigating just how popular this once-in-a-lifetime eclipse could be.
"Twelve million people live on the path of totality across the whole country," Speck says. "There are four times as many people that live within 100 miles. There are seven times as many people that live within 200 miles."
Any other day, most of these spots would be off the beaten path. In August, they'll be the best place for millions of people to see the event. Nearby cities and towns are bracing for huge crowds.
Experts will also join the temporary migrations. Eclipses aren't just a spectacle — they're a rare chance to investigate the sun, moon and our own weather.