A total solar eclipse is when the moon moves between the sun and Earth, lasting for up to about three hours from beginning to end, according to NASA. The lunar shadow will darken the sky, temperatures will drop and bright stars will appear at a time that is normally broad daylight.
Retired NASA astrophysicist and photographer Fred Espenak said the experience usually lasts for just a couple minutes, but it's truly out of this world.
"It is unlike any other experience you've ever had," Espenak, popularly known as Mr. Eclipse, told ABC News. "It's a visceral experience; you feel it. The hair on your arms, on the back of your neck stand up. You get goosebumps."
"You have to be there," he added.
Espenak said a total solar eclipse can last as long as seven minutes. For the Aug. 21 eclipse, NASA anticipates the longest period when the moon obscures the sun's entire surface from any given location along its path to last about two minutes and 40 seconds.