The path of the eclipse across the U.S. on Aug. 21. Los Angeles Times infographic

This summer, darkness will fall across the face of America. Birds will stop singing. Temperatures will drop. Stars will become visible in the daytime sky.

In about 100 days, a total solar eclipse will sweep across the continental U.S. for the first time since 1918. Astronomers are calling it the Great American Eclipse.

For solar astronomers, the eclipse offers three minutes to collect as much data as possible about the sun’s usually hidden outer atmosphere.

Some will take measurements from the sky; others have engaged vast networks of citizen scientists to track the eclipse as its shadow moves across the ground. Ultimately, they hope their findings will tell them more about the sun’s magnetic field, the temperature of its outer atmosphere and how energy moves through the star and out into space.

The sun is so bright that even when 99 percent of it is covered by the moon, the remaining 1 percent is still bright enough to make the sky blue, said Jay Pasachoff, an astronomer at Williams College in Massachusetts. But during a total solar eclipse, the moon completely obscures the face of the sun, causing the daytime sky to darken by a factor of 1 million.

On Aug. 21, what’s known as the path of totality will cut a 60-mile-wide arc across the United States, beginning in Oregon at 10:15 a.m. local time and ending in South Carolina about an hour and a half later.

Researchers from the Harvard-Smithsonian Center for Astrophysics plan to study the corona from an airplane flying at 49,000 feet.

The group, led by solar physicist Ed DeLuca, is building an instrument that will allow them to examine the solar atmosphere in infrared wavelengths. Their ultimate goal is to better understand the magnetic fields in this outer region of the sun – in part because this is where coronal mass ejections originate.

“Measuring these magnetic fields is really useful for understanding how energy is stored in the corona and when we expect it to be released,” DeLuca said. “Once we understand that, we can make better space weather predictions.”