– Planets and moons and stars circle seamlessly in the darkness, unnoticed, until their paths cross in a way that can’t be ignored.

On Aug. 21, 2017, the moon will slip between the sun and Earth, casting a shadow that will create the first full solar eclipse over the U.S. in 38 years.

In a swath of country from South Carolina to Oregon, darkness will reign in the middle of the day for a full 2 minutes and 40 seconds, beginning at 12:25 p.m. Central time.

“If you can only see one in your lifetime, the one to see is August 21, 2017,” said Sam Storch, a retired astronomy professor. “This is something scheduled by the motions of objects in the heavens. There is nothing humans can do to make it come sooner or later. There is no do-over.”

Full solar eclipses viewable from populated areas are rare. The last full solar eclipse in the U.S. was in 1979, but it covered only five states.

People from all over the world plan to travel to areas within the 100-mile swath of totality to see the show.

“You have so many people born since the last one occurred who have never seen a total eclipse of the sun. It’s really an opportunity,” said Paul Maley, an astronomer and former NASA scientist who organizes astronomy tours worldwide.

Maley is leading a group of about 100 people with EclipseTours.com next year to Grand Island, Neb. — a town he chose because of its proximity to the central path of the eclipse, but also because it is close to major roads in case cloud cover forces the eclipse seekers to change locations quickly.

In Carbondale, Ill., where NASA says the absolute maximum totality will occur, the town has established an eclipse plan and task force to prepare the city of 26,000 for an onslaught of tourists.

Town concerns range from whether there will be enough bandwidth to accommodate mobile devices to whether there will be enough lodging. The town has 513 hotel rooms and two bed-and-breakfasts, according to the “first phase” of the eclipse plan.

And lucky Carbondale, it is also in the path of the April 8, 2024, total solar eclipse.

Alex Young, associate director of the Heliophysics Science Division at NASA Goddard Space Flight Center in Maryland, plans to be in Carbondale for the eclipse, which will be his first.

“Total solar eclipses are not rare. They happen all over the world, but they are rare in populated areas,” Young said. “That’s what makes this one so exciting. Having one from Oregon to South Carolina is phenomenal.”

Everyone in North America will see some kind of eclipse. In Florida, about 81 percent of the sun will be covered by the moon.

In the direct path of the eclipse, it will be as if night falls — mosquitoes may begin to nibble thinking it is dusk, temperatures will dip, animals will settle, stars will shine. And the corona of the sun will appear as a ring of fire around the moon.