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What science can learn from a total solar eclipse


160 seconds is a long time in heliophysics


The Sun’s corona visible during a total solar eclipse in 1991.
The Sun’s corona visible during a total solar eclipse in 1991.
Roger Ressmeyer / Corbis / Getty

On August 21, when the first total eclipse of the Sun to hit the continental United States in 38 years cuts a swath of darkness across the heart of the country, tens of millions will flock into its 110-kilometre-wide path to view the event.

Among the throng will be scientists, seeking to use the 160 seconds in which the Sun is obscured by the Moon to make discoveries about everything from atmospheric dynamics to the prospects for life on Mars.

One of the most exciting experiments, says Catherine Lanier, associate director for NASA’s Space Grant program at Oregon State University (which happens to be situated within the path of totality), will be an effort to study the eclipse from balloons launched to altitudes of 30,000 metres (100,000 feet) at 55 points along the path of totality.

The results will not only provide dramatic live-stream videos (via NASA TV) but will be the first time an eclipse has ever been watched from this angle, with 360-degree cameras studying what is happening in the sky, on the ground and in the clouds.

Other researchers will use weather balloons to record atmospheric data. “It’s trying to learn about how the atmosphere responds,” Lanier says.

Some of the NASA balloons will carry bacteria strains comparable to ones that might survive on Mars.

The temperature and pressure conditions at 25,900 metres (85,000 feet) are similar to those on the surface of Mars, explains Alex Young, of the Heliophysics Science Division at NASA’s Goddard Space Flight Center in Greenbelt, Maryland: “Flying the bacteria to the edge of space provides a unique opportunity to examine how bacteria are able to survive in harsh Martian conditions.”

Another team, financed by spaceweather.com, will also be launching balloons, using the eclipse as an opportunity to measure high-elevation cosmic rays.

Using high-elevation balloons to monitor radiation levels at the edge of space, these researchers have recorded a 10% increase in cosmic-ray counts since late 2014. All of the measurements have been taken from one location, above California, so they want to know what is happening over the rest of the country: “The solar eclipse gives us a chance to find out.”

Measuring cosmic rays during the eclipse also enables them to eliminate the Sun as the source, because the Moon will block its radiation during the eclipse.

Other astronomers will use the eclipse as an opportunity to turn their instruments on Mercury, whose proximity to the Sun makes it hard to observe. This is a rare chance to use infrared instruments to make thermal maps of Mercury’s surface temperature, particularly on its night side.

“How the temperature changes across the surface gives us information about the thermophysical properties of Mercury’s soil down to depths of about a few centimetres, something that has never been measured before,” says Constantine Tsang, a planetary scientist from the Southwest Research Institute (SwRI) in Boulder, Colorado.

The most important part of any total solar eclipse, though, is the chance to view the Sun’s corona — the ghostly glow around it that is otherwise too dim to be seen against the daytime sky.

Even though astronomers now have a lot of space-based instruments to study the corona, observing it from the Earth — especially from high-flying airplanes — provides opportunities that can’t be done from space.

Airborne cameras can provide higher-resolution high-speed images than space-based instruments, says Amir Caspi, a plasma physicist from SwRI.

Eclipse science may also include a healthy dose of social psychology, because the once-in-a-lifetime chance to see the solar corona is why millions of Americans will brave horrendous traffic jams —forecast to be the worst in history — to flock to the path of totality.

“It’s the most beautiful natural phenomena most people can witness,” says Randal Millstein, an astronomer at Oregon State University. “It’s an experience that’s been shared by human beings for as long as we’ve looked up at the sky.”

Seeing an eclipse, he says, is a bond that extends across the eons, and is emotionally and psychologically deep: “You’ll find people who will cry. Others will laugh. Some will sing. Some will fall back on the ground. It’s that kind of experience.”

Contrib ricklovett.jpg?ixlib=rails 2.1
Richard A. Lovett is a Portland, Oregon-based science writer and science fiction author. He is a frequent contributor to COSMOS.
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