Millions of one-day astronomers gathered Monday in hundreds of cities, towns and parks along a 70-mile-wide "path of totality" as the much-ballyhooed Great American Eclipse began its astronomical march across the nation.

The total solar eclipse — the moon completely obscuring the sun — started along Oregon's west coast shortly after 10 a.m. PT. The total eclipse will wrap up along coastal South Carolina before 3 p.m. ET.

The picturesque town of Silverton, Ore., began to fill with eclipse-watchers several hours ahead of the celestial event. Susan Gurton was heading to the local high school for an eclipse viewing. The assistant director for education with the National Radio Astronomy Observatory in Charlottesville, Va., has worked at several eclipses in the past.

"But this time my kids said 'Can we just go?' So this one I'm not working," she said.

In Weiser, Idaho, eclipse festival chairman Patrick Nauman was expecting 60,000 visitors for the eclipse. That's about 10 times the town's population. Sara Bronson, who grew up in Weiser, called the influx of tourists "spectacular."

“I think it's awesome," she said. "It's exactly what we've been wanting ... to show off our community."

The total eclipse is a brief event, lasting less than three minutes even in prime locations. The entire nation will be treated to a partial version of the phenomenon.

For most eclipse watchers, weather largely won't be a problem, AccuWeather meteorologist Brian Thompson said. But it was raining in parts of Missouri and cloudy in much of South Carolina as the partial eclipse grew closer to totality.

NASA was livestreaming the eclipse from Jefferson City, Mo., where the weather was holding up and crowds were happy to see 7,500 pairs of eclipse glasses NASA was giving away. NASA experts were on hand to explain what was going on overhead in real time.

"We'll talk about Bailey beads (dots of light around the moon) and about the four different planets we should be able to see with the naked eye at peak totality," NASA spokeswoman Debbie Lockhart said.

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Nashville was a big draw for eclipse fans, and the Kimpton Aertson Hotel booked an astronomer to provide educational value to the experience. Janet Ivey, host of the Nashville science show Janet’s Planet, said interest has been phenomenal across the city. 

"The solar eclipse is science’s Christmas and Super Bowl all wrapped up into one,” Ivey said.

In Anderson, S.C., Gregory McClain of Atlanta was setting up for the show with a party of nine people. The group of family and friends was set up at eclipse viewing hotspot Green Pond Landing 10 hours in advance of the total eclipse.

"My friend told me back in February about the eclipse," McClain said, eyeing his group. "Everyone was like 'We're not gonna see no eclipse.' Now look around!"

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In Charleston, S.C., the last major city in the path of totality, and business was booming despite a dark weather forecast. A thick layer of clouds -- with only a few peeks of sun -- covered the downtown sky as the partial eclipse began. Still, people were in a festive mood on their blankets and chairs at Marion Square, cheering during the brief breaks in the cloud cover.

Taxi driver Santel Powell, who was busy shuttling visitors to and from the airport, said he's seen license plates from states across the country. The lifetime Charleston resident said the city has been preparing for the big event for months.

Charleston coastal towns such as Edisto Beach, located about an hour southwest of Charleston, also are riding the wave. A group of friends from Maryland rented a house there for the week just to watch the sun disappear.

"When we learned of the solar eclipse, the middle-age nerds among us were giddy with excitement," said Allison Leaver of Silver Spring, Md. Added Jenny Kelley, also of Silver Spring: "It's a long way to drive for two minutes of astronomical awesomeness."

Contributing: Elizabeth Weise, USA TODAY; Adam Tamburin, The Tennessean, Ron Barnett, The Greenville (S.C.) News; Natalie Shaver, KTVB-TV in Idaho; Natalie Pate, Salem, Ore., Statesman Journal; Wes Johnson, Springfield (Mo.) News-Leader