It's an act of nature that has caused hundreds of thousands of people to flood into Middle Tennessee.
"A total eclipse is caused when the moon gets in between the earth and the sun," said Robert "Hoot" Gibson, a retired NASA Astronaut.
It's an unusual eclipse that's going to cross the entire country, and everyone has been hoping to catch it when it happens.
"I planned this trip back in February, back February-April range," said one woman.
This isn't Hoot's first time preparing to watch a total eclipse.
"I had experience previously chasing the total eclipse of the sun that happen February 26, 1979," he said.
Hoot took off in a NASA jet from a Montana Air Force base and raced the eclipse until he landed at a South Dakota Air Force base.
"Managed to get over four minutes of totality by racing along at 600 mph with the shadow of the moon during that eclipse," said Hoot.
Though it's a natural event that doesn't need much advertising, most people have been making sure they're outside to watch history.
"They're not very common, and this one, since it's crossing our entire country, has generated just a tremendous amount of interest and a tremendous amount of excitement," said Hoot.
There's still another day of excitement at the Adventure Science Center on Sunday from 9 a.m. to 5 p.m.
Organizers confirmed Monday's event is sold out.
