Eclipse

Dark skies ahead

Great American Eclipse blocks the sun Aug. 21

Posted 8/14/17

It’s a mighty big fuss for what amounts to a shadow.

The moon butts its way in between the Earth and the sun Aug. 21, casting its shadow across the continental U.S. from sea to sea.

A cross-continental U.S. total eclipse like this hasn’t …

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Eclipse

Dark skies ahead

Great American Eclipse blocks the sun Aug. 21

Posted

It's a mighty big fuss for what amounts to a shadow.

The moon butts its way in between the Earth and the sun Aug. 21, casting its shadow across the continental U.S. from sea to sea.

A cross-continental U.S. total eclipse like this hasn't occurred since 1918. And the rare event comes with a special name: The Great American Eclipse.

"That's what they call it, because everyone in the United States will get to see something, at least a little bit of it," said Damon Olsen, astronomy instructor at Littleon's Arapahoe Community College. "Everyone in the U.S. will see it, plus Canada, Mexico and the Caribbean. They'll all see something."

Along the Front Range, the moon begins creeping over the sun at 10:23 a.m., covering more than 90 percent of the sun just before noon.

By 1:23 p.m. the Great American Eclipse should have moved out of Colorado.

Schools, libraries and parks across the Denver Metro area are hosting viewing events, complete with glasses, telescopes and crafts for kids.

At Westminster's campus of Front Range Community College, the school will have multiple filtered telescopes, eclipse glasses and other displays.

"We will have a telescope, solar viewing glasses, pinhole cameras," said Clara Wente, chair of the science department at Front Range Community College's Westminster campus. "We may have astronomical binoculars, which are binoculars with special solar filters."

The path matters

Like most professional sky watchers in Colorado, Wente said she won't be anywhere around here when the eclipse begins. She's headed north into the path of the deepest part of the shadow, total coverage of the sun by the moon.

"Like millions of other people, I'm going to be at the eclipse," Wente said. "Basically, everyone else here is going to Wyoming, so my husband I decided to go Nebraska. Either way works, but we didn't want to get stuck on traffic on I-25."

Solar eclipses come in three varieties: total, annular and partial.

A partial eclipse occurs when any part of the moon covers the sun, and that can happen as often as five times per year.

Annular eclipse happen when the moon moves completely in front of the sun but, because of the moon's elliptical orbit, it is too far from the Earth to completely block the sun. An annular eclipse results in a bright ring of sunlight around the moon.

Total eclipses, like this one, are the rarest, typically occurring somewhere on Earth every 18 months or so.

The Aug. 21 solar eclipse begins about 9:55 a.m. mountain time somewhere over the North Pacific Ocean, northwest of Hawaii and just east of the International Dateline.

It makes landfall on U.S. soil at about 10:04 a.m. Mountain Time just west of Salem, Oregon, reaching totality - total blockage of the sun by the passing moon - at about 11:16 a.m Mountain Time there.

From there, it follows a looping diagonal path southeast across the country's midsection, through Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennesee and South Carolina.

Eclipse totality comes closest to Colorado before noon. Casper, Wyoming, should go dark at 11:43 a.m.; Grand Island, Nebraska, at about 11:59 a.m. Mountain Time. The total eclipse will last more than two minutes in each location.

The eclipse finishes with the U.S. and leaves the continent at 12:48 p.m. Mountain Time just north of Charleston, South Carolina. It's completely finished at 12:55 p.m. Mountain Time out over the Atlantic Ocean.

Those in the direct path will see the sun completely covered, all but a wispy ring. That is the sun's chromosphere or atmosphere and seeing that is why eclipses matter to astronomers.

"It's one of the rare times you can actually view the sun's atmosphere," Wente said. "It's one of the advantages of having a total eclipse. It's the very lowest atmosphere, right above what we think of as the surface of the sun. It's colored red but you can't normally see it because the sun is so bright."

It's also the most breathtaking for everyone because a 100 percent total eclipse is as different from anything else as night and day - quite literally, Wente said. Under totality, the sky goes dark and stars will be visible.

A crescent sun

Colorado is out of the path of totality and Wente said sky observers should not expect mid-day darkness here. From the perspective of viewers in Westminster, the moon will cover nearly 93 percent of the sun; in Highland's Ranch it's about 92 percent.

"The sun's wattage, what we actually see, is about 1,300 to 1,400 watts per square meter," she said. "A light bulb is 100 watts. So even 10 percent of the sun's light will be a lot. I'm expecting it, personally, to be like a cloudy day."

There should still be quite a show.

"I think the amazing thing will be just to see the sun as a crescent, to see the moon over on top of the sun," she said.

The eclipse maximum will be over quickly, she said, finished here in minutes.

"Part of the fun is the whole process, the moon moving in over the sun," she said. "We won't get that totality, but will get to follow along, up to that 90-plus percent."

And if you miss it, don't worry. There will be another Great American Eclipse on Aug. 12, 2045 - and this time, Denver will be in the path of the totality.

"It's just like this one, but 200 miles to the south," she said. "It'll come right through the center of Colorado and we only have to wait another 28 years."

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