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Astronomy lovers plan for 'The Great American Eclipse'

| Judy Berthiaume

Dr. Paul Thomas was on a mountaintop in in Australia in 1976 when he saw a total solar eclipse for the first time.

“It was a stunning experience,” says Thomas, a UW-Eau Claire professor of astronomy. “I had seen partial solar eclipses before, but the abrupt change in light and temperature, and the dramatic sweeping movement of the moon's shadow across the earth were overwhelming.”

He hopes to have an equally stunning experience Aug. 21 — though this time in Missouri instead of Australia — when a total solar eclipse will sweep across the United States for the first time in decades, creating what many astronomers are describing as the biggest astronomical event in the United States in many years.

A total solar eclipse occurs when the moon passes between earth and the sun, entirely blocking the view of the sun.

The 2017 total solar eclipse will be the first to travel coast-to-coast in America in nearly a century, and the first in the U.S. since 1979, when it was visible only in the northwestern corner of the country.

The 70-mile wide path that will fall directly in the shadow of the moon — described by Thomas as the eclipse trail — will first appear at about 10:15 a.m. Pacific time in Oregon and move west across the country to South Carolina, where it will appear at about 2:49 p.m. Eastern time.

Over approximately 90 minutes, it will pass through Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina. Each spot along its trail will experience a little more than two minutes of total darkness.

While millions of people will see the total eclipse, most of the country will see only a partial eclipse, which is why Thomas and many other astronomy lovers plan to travel to areas within its path.

For those staying closer to home, UW-Eau Claire will host an eclipse-viewing event (open to the public) from noon-2:30 p.m. Aug. 21 in the outdoor amphitheater in front of Davies Center.

Astronomers expect the best viewing in Eau Claire — the maximum eclipse — to be a little after 1 p.m.

Faculty will have two or three telescopes set up for viewing. They also will have eclipse glasses (required for anyone viewing the partial or total eclipse) for visitors to use.

Thomas says that in the Eau Claire area, the maximum that the moon will cover the sun will be 82 percent. For a little more than an hour before and after this time, the moon will be covering part of the sun, he says.

Dr. Paul Thomas took a few minutes to share more information about the total solar eclipse to help explain the phenomena, as well as its significance.

Tell us more about a total solar eclipse.

A total solar eclipse occurs when the moon passes in front of the sun, as seen from the earth.

It's a coincidence that the apparent size of the moon in our sky is about the same as the apparent size of the sun — both are about half a degree across. This is because the moon is about 400 times smaller than the sun, but the sun is 400 times farther away.

When a total solar eclipse occurs, it's visible from not just a single point on the earth, but a set of points along an "eclipse trail." This is because the earth rotates, allowing many locations to see the sun covered by the moon.

An eclipse trail is typically 65-70 miles wide and can extend for over 1,000 miles. Outside of this area, you may see a partial solar eclipse.

What is it like to be within the eclipse trail?

A total solar eclipse is a stunning event.

If you're on a high location, you can see the moon's shadow sweep toward you. The sky turns a dark blue, similar to dusk.

You can see the corona, the outer atmosphere of the sun that is normally overwhelmed by the sun itself.

The temperature will drop noticeably. Everyone I know who has seen a total eclipse agrees that it is a very memorable event.

Why is this one such a big deal?

The Aug. 21, 2017, eclipse trail lies across the entire United States, from coast to coast (Oregon to South Carolina). Many astronomers are calling this "the Great American Eclipse.”

No doubt, millions of Americans will drive to the eclipse trail to see the total eclipse, which will last for a maximum of 2 minutes 40 seconds.

A total solar eclipse has not been seen in the contiguous U.S. since 1979, and a coast-to-coast eclipse has not happened since 1918.

Partial eclipses were visible in Eau Claire as recently as 2012.

How often does this kind of an event happen?

Total solar eclipses occur several times a decade, but you have to be at the right location to see them.

Astronomers who study solar eclipses are used to world travel!

There were several solar eclipses visible from some parts of the U.S. in the last decade, but they were all annular (meaning that the moon was too far away from earth on its elliptical orbit to totally cover the sun).

A total solar eclipse in February 1979 was visible from the Northwest of the U.S. (Washington, Oregon, Idaho and Montana).

The last time a total eclipse was visible from coast-to-coast of the U.S. was June 8, 1918.

The next U.S. total solar eclipse, on April 8, 2024, will pass over the central U.S., from Texas to New Hampshire.

Unfortunately, Eau Claire will not see a total eclipse next time either. However, the 2024 eclipse path will pass through Illinois, Indiana and Michigan.

A region containing the towns of Carbondale, Illinois, and Paducah, Kentucky, will see both the 2017 and 2024 total solar eclipses. Two total eclipses in seven years!

How can you safely watch a solar eclipse?

While the period of totality is safe to watch, you should never look at any part of the uncovered sun directly.

The American Astronomical Society website states:

The only safe way to look directly at the uneclipsed or partially eclipsed Sun is through special-purpose solar filters, such as “eclipse glasses” or handheld solar viewers. Homemade filters or ordinary sunglasses, even very dark ones, are not safe for looking at the Sun. To date, five manufacturers have certified that their eclipse glasses and handheld solar viewers meet the ISO 12312-2 international standard for such products: Rainbow Symphony, American Paper Optics, Thousand Oaks Optical, TSE 17, and Baader Planetarium (AstroSolar Silver/Gold film only).

However, you can also view the eclipse safely using projection.

To do this, get a sheet of cardboard or foam core and punch a small hole in it with a pencil. Hold it facing the sun and look away from the sun to the shadow cast on the ground. If you move the sheet back and forth, you should see an image of the sun. This will allow you to see the shape change as the moon moves in front of the sun.

Other than being cool to see, are there other reasons solar eclipses matter?

The study of the solar corona, which can only be seen in the absence of the overwhelming light from the sun's disk, was historically a good scientific reason for astronomers to travel to see solar eclipses.

This is not important now that we have satellites constantly observing the sun from orbit that can block out the sun's disk with coronagraphs (special telescopes with an obstruction that blocks the sun’s light). Two current missions are the U.S.-European SOHO and the American SDO, and they both post current corona images on the web.

However, there is still scientific work to be done understanding the complex changes in the many layers of earth's atmosphere that occur as the moon's shadow sweeps across the eclipse path.

Where can people go to get more information?

A really good web site is Eclipse

Other websites:

Sky and Telescope magazine

American Astronomical Society

PBS NOVA Eclipse over America

Any other thoughts to share?

If you ever get a chance to see a total solar eclipse, you should take advantage of it!

The experience is so much more intense than a partial solar eclipse.

Photo caption: Dr. Paul Thomas (right) will travel to Missouri to experience the Aug. 21 total solar eclipse. UW-Eau Claire will host a viewing event on campus, helping people safely view the partial eclipse.