ST. LOUIS COUNTY • The total solar eclipse that will pass through the St. Louis region was still more than 60 days away. But that didn’t dissuade thousands of people from making their way to Queeny Park Saturday to prepare for the big celestial party.

The line to get into the park’s Greensfelder Recreation Complex snaked out of the doors and into the parking lot. Inside, going through the crowd at St. Louis Solar Eclipse Expo was like navigating a busy day at Busch Stadium. Organizers said they had pre-sold 8,000 tickets for the event.

Hundreds of people squeezed past each other and dozens of exhibitors hawking information on events, telescopes and protective eyewear. All of them had the big moment on their minds: 1:16 p.m. on Aug. 21.

That’s when the moon will completely block out the sun across the southern swath of the St. Louis region, which sits in the path across North America cast by the moon’s shadow. The temperature will drop by about 10 degrees Fahrenheit, the wind will pick up as the atmospheric pressure changes and birds will head to roost for what turns out to be a very short night.

“I think it’ll be cool to see the sun disappear for a while,” said Luke Latham, 13, who was at the expo with his brother, Dean Latham, both students at Chaminade College Preparatory School.

Their grandpa, a professional astronomer, keeps them up to date on all things eclipse. They were looking forward to heading to Trout Lodge to watch the first total eclipse to run through the area since the 15th century.

“We need to find out about school first,” their mother, Dawn Latham, reminded them.

The eclipse is on a Monday, and many schools are planning to make a day of it. Joe Feld, a physics teacher at De Smet Jesuit High School, was at the expo to cull a few lesson ideas. Feld said he expected more than just science lessons: math, history, even theology can all weave the event into their curriculum for a few days.

“An event like this crosses all of your disciplines,” he said.

He also wanted to get a handle on safety. There’s only about 2 minutes and 30 seconds at the center of the eclipse path when the sun is completely blocked out and it’s safe to look at where the sun was. In many parts of St. Louis County, it will be about a minute shorter.

“We want to make sure we understand all the risks, but we don’t want to miss the opportunity for the students to learn,” Feld said.

Angela Speck, an astronomy professor at the University of Missouri-Columbia, explained that “there’s nothing intrinsically dangerous about an eclipse.” It’s just that when there’s no eclipse, people generally don’t try to stare at the sun.

A partial eclipse will start a little before noon and run until about 2:45 p.m. It’s that tiny two minute or so window starting about 1:16 p.m. when it’s safe to take off protective eyewear and observe the sun’s usually hidden corona, the flickering jacket of gasses that make up the star’s outer atmosphere and are visible to the naked eye during a total eclipse. Normally hidden stars will be visible, too.

John Weis of NASA’s Marshall Space Flight Center recommended telling students to put their protective glasses back on about 15 seconds before the duration of totality ends about 1:19 p.m. Times vary depending on where you are, and it can vary a lot across just a short distance. NASA maintains an interactive map where users can find the exact start and stop time of the eclipse at different spots. Find it at eclipse2017.nasa.gov.

Of course, students may be more apt to forget instructions when they are plunged into total darkness for a minute or more.

“Ninety percent of the general public will lose whatever they were thinking,” Weis said.

The last total eclipse in the U.S. was in 1979, but it crossed from Washington to North Dakota and then north through Canada.

Solar eclipses, even total solar eclipses, aren’t especially rare, Speck, the astronomy professor, reminded an audience Saturday. You just have to be in the right place at the right time to see them, and sometimes that’s in the middle of the ocean or in sparsely populated areas.

Millions of Indonesians witnessed one last year. But most people are not so lucky.

“Most people never get to see them in their lifetimes,” Speck said. “Now we have this one going over our heads and we don’t have to go anywhere.”

Jacob Barker • 314-340-8291

@jacobbarker on Twitter

jbarker@post-dispatch.com

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