The Great American Total Solar Eclipse will take place on Aug. 21 as the biggest celestial event in four decades. There is high excitement among astronomers, stargazers, and casual space watchers as it is the first total solar eclipse in the U.S. mainland since 1979.

Starting in the late morning, the partial eclipse will linger till the early afternoon of 1 p.m. noon.

"It's a tremendous opportunity," noted eclipse expert Jay Pasachoff, an astronomer associated with Williams College in Massachusetts.

Pasachoff said the total eclipse will be a chance to see the universe changing around the viewer.

The last time the U.S. mainland was darkened by a total solar eclipse was on Feb. 26, 1979. The August event, however, will be more special as it is "readily available to people from coast to coast," Pasachoff added.

In many places, the preparedness has already begun. People are buying viewer glasses for a dollar. The Southern Illinois University Carbondale has announced a weekend of events that will conclude with a public viewing at Saluki Stadium.

Scientists are also planning to send up weather balloons to collect data.

Traffic plans are now being reworked to handle the rush of thousands of sun gazers gathering at one place.

What Will Happen?

On Aug. 21, Monday, thanks to the moon's positioning before the sun, much of the sun's disc will be blocked and a gradually evolving solar eclipse will unfold, moving from partial eclipse to full eclipse.

When the total solar eclipse happens, the moon blocks the bright face of the sun and what is on view will be a faint solar atmosphere, called the corona.

After half an hour, the sun will turn bright again but appear with a diminished crescent-like shape. In the remaining minutes, the sun will return to the normal and the eclipse will be through.

In the United States, a 75-mile-wide swatch from coast to coast will see the moon blocking the entire sun during the event. There will be brief darkness barring brighter stars and planets shining. Columbia will be one of the best viewing spots.

Eye Protection

From Oregon to South Carolina the stretch of land 70 miles wide will have this rare celestial show making the skies turn dark.

For those on the "path of totality," the celestial event will be an unforgettable experience. As for the rest of the continental United States, there will be a 55 percent partial eclipse, and complete darkness may not be there. Pasachoff advised eclipse enthusiasts to use eye protection filters at all times even while checking whether the eclipse is happening.

NASA Study

Meanwhile, NASA is funding 11 scientific studies to leverage the total solar eclipse opportunity as a brilliant sight in the sky for collecting data.

"When the moon blocks out the sun during a total eclipse, those regions of Earth that are in the direct path of totality become dark as night for almost three minutes," said Steve Clarke, director of the Heliophysics Division at NASA Headquarters in Washington, D.C.

He said the best-observed eclipse will be a unique opportunity to learn about the sun and its effects on Earth and their interaction, thanks to the eclipse's long path over land.

As the eclipse path crosses the United States from coast to coast, ground-based observations for more than an hour can complement the data provided by NASA satellites.

To study corona in detail under visible light, the total solar eclipse will be a great opportunity. In most studies, corona's inner regions had been a missing link in understanding space weather. The eclipse also offers a brilliant opportunity to study Earth under uncommon conditions.

When the sun is blocked by the moon the reduction in light and temperature as quick-changing conditions on the ground will affect weather, animal behavior, and vegetation.

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