CHEYENNE, Wyo. (AP) — Where's the best place to watch next year's eclipse? If you're thinking the grand open spaces of Wyoming, you have plenty of company.

Hotel rooms across the Cowboy State are going, going, gone, well over a year before the arrival of the first total solar eclipse to be seen from the mainland U.S. in almost four decades.

A national astronomy convention has reserved Casper's largest hotel. International guides plan eclipse-oriented tours of the Yellowstone region. Jackson Hole is bracing for big crowds, and Native American tribes are promoting their heritage as the perfect backdrop for the rare natural event.

Tourism boosters are giddy. They've done little to market Wyoming as an eclipse destination, with millions already visiting Grand Teton and Yellowstone each year, and yet even campsites are being claimed more than a year before eclipse day, Aug. 21, 2017.

"What's hot on everybody's mind is, what's the attendance number?" said Brook Kreder with the Casper Area Convention and Visitors Bureau.

She projects 20,000 visitors, one-third of Casper's population. With an influx like that, many more locals might join in the profits. "We have had some people inquire about putting their personal bedrooms up on Airbnb," she said.

Some are calling this the Great American Eclipse, because the moon's shadow will cross Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina before heading out over the Atlantic.

Communities from coast to coast are already arguing for bragging rights as the best place to watch:

— Madras, Oregon, claims its high-desert setting 100 miles southeast of Portland gives the best odds for clear weather. The city plans an Oregon SolarFest, with camping, music and beer gardens.

— North Platte, 275 miles west of Omaha by Interstate 80, bills itself as a safe and accessible viewing place in the Nebraska Sandhills region.

— The sun, moon and Mississippi River will meet 80 miles south of St. Louis in Perry County, Missouri, local promoters say.

— Nashville will be the biggest city under total eclipse but Hopkinsville, Kentucky, an hour north, boasts it will have the greatest degree of eclipse anywhere, meaning it will remain "total" for longer.

— South Carolina offers the closest eclipse-watching for 100 million people on the East Coast, right before the moon's shadow crosses into the Atlantic Ocean, assuming summer rain clouds don't block the view.

Solar eclipses, which happen when the moon passes directly between the Earth and sun, are not rare, but they seldom happen in such easily accessible places.

A roughly 65-mile-wide zone, called the path of totality, will offer the best viewing as the moon's shadow races over the Earth's surface at more than 2,000 mph. Stars and planets come out, and the sun's corona glows in a perfect circle around the dark side of the moon as the effect of a sunset appears in all directions.

Depending on the location, the eclipse will be total for less than 30 seconds to as long as 2 minutes, 41 seconds.

"It gets darker and darker and darker. And what's weird is, the temperature drops and then wildlife becomes mysteriously quiet," amateur astronomer Lowell Lyon explains. "All of a sudden — boom! — it suddenly gets dark."

Astrocon2017, next year's annual convention of more than 240 U.S. amateur astronomy groups in the Astronomical League, will bring dozens of experts to Casper over the four days leading up to the eclipse. Lyon, who sells insurance in Salt Lake City by day, is organizing the event.

Even without astronomical phenomena to attract them, tour groups in Jackson Hole often reserve blocks of hotel rooms a couple years ahead of the winter and summer peak seasons.

People hoping to watch the eclipse from the foot of the Teton Range began booking rooms even further in advance, said Clarene Law, who owns four Jackson hotels.

"Some of these photographic groups got in here before my staff realized it was the eclipse," Law said. She said she doesn't plan to raise rates — by much — for the few rooms she has left.

One company that provides eclipse-viewing tours worldwide plans several multi-day, multi-state packages that will take hundreds of travelers to Tennessee, northwest Wyoming and Oregon to watch the eclipse. Past customers of the Prescott, Arizona-based TravelQuest International who have traveled as far as Bali, the Faroe Islands and Ethiopia have signed up for next year's trips, President Aram Kaprielian said.

"This time, they're traveling with their children and with their children's children. So we're getting these generational groups that are joining us," he said.

One eclipse-watching advantage in Wyoming: A two-lane highway, U.S. 26, crosses the state entirely within the path of total eclipse. In case of clouds, eclipse watchers seeking clear skies will be able to drive more than 400 miles without leaving the prime viewing zone. All while keeping their eyes on the road, of course.

The route also crosses the Wind River Indian Reservation in central Wyoming, where the Northern Arapaho and Eastern Shoshone tribes plan eclipse-oriented dances and eclipse-day tours to the sites of ancient petroglyphs, said Casey Adams, a spokeswoman for the Wind River Visitors Council.

"It can be a more personal experience. It's not going to be crowded. You can go find your own special little corner of Fremont County and take it in with just your close friends and family by your side," Adams said.

Or, you might join the lively, festival atmosphere in Lander, a funky outdoors town at the foot of the Wind River Range, she said.

A lonesome Wyoming mountaintop would offer a spectacular view, but Lyon, the convention organizer, wants to be with his other dedicated stargazers.

"Just to hear the reaction of the crowds and the wild cheers that will go up," Lyon said. "It's kind of an adrenaline rush when you're in a mass of people all sharing that experience."