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Millions of Americans will enjoy the spectacle of the total solar eclipse later this month, and scientists will be hard at work. NPR's Nell Greenfieldboyce has more about this rare opportunity to learn more about our sun and its relationship to Earth.
NELL GREENFIELDBOYCE, BYLINE: People have been observing total solar eclipses for ages. The first-century Greek scholar Plutarch described the darkening of the sun. So did the Babylonians on their clay tablets and ancient imperial astronomers in China and on and on and on. What could there possibly be left to learn?
JAY PASACHOFF: I get asked all the time, why are we still doing eclipses for scientific purposes after all this time?
GREENFIELDBOYCE: Jay Pasachoff is an astronomer at Williams College who chairs the International Astronomical Union's Working Group on Solar Eclipses.
PASACHOFF: There are still whole parts of the sun that can't be seen from satellites and that we just see better at eclipses.
GREENFIELDBOYCE: When the moon slips in front of the sun and blocks its light, what's revealed is the sun's outer atmosphere. It looks like a glowing ring or crown called the corona. Matt Penn is an astronomer at the National Solar Observatory in Arizona.
MATT PENN: The corona, I think, is the most beautiful thing you can see in the sky. The corona is just fantastic and filamentary and delicate and awesome.
GREENFIELDBOYCE: Now, scientists have ways to look at the corona any old time. They can put a disc in their telescopes to create an artificial eclipse. But the moon can do something those little discs can't. When the moon perfectly aligns to block the sun, it reveals a special place called the inner corona. There's a lot of activity there related to the so-called space weather, which can affect Earth's electric grids and communications systems. A total eclipse lets scientists see the inner corona. But Penn says from one spot on the ground, the view lasts just a couple minutes.
PENN: And the corona's big. It changes, but slowly. And in two minutes you really can't see changes that we want to study in the solar wind.
GREENFIELDBOYCE: That's why Penn has been organizing Citizen CATE, the Continental-America Telescopic Eclipse Experiment. Trained volunteers will be positioned at 68 sites across the entire 2,500-mile path of the total eclipse. As the moon's shadow crosses the country, those volunteers will use identical telescopes to take photos of the corona. Penn says when the images get stitched together into a continuous movie...
PENN: We can observe the corona for 93 minutes and therefore see changes that we wouldn't normally otherwise detect.
GREENFIELDBOYCE: This is just one of the many science activities planned for the eclipse. In addition to ground-based telescopes, researchers will watch with the help of satellites, airplanes and high-altitude balloons. Angela Des Jardins at Montana State University is head of the Eclipse Ballooning Project. She says more than 50 balloons will send back live video of the eclipse from the edge of space. Balloons will also collect information on the response of the Earth's atmosphere.
ANGELA DES JARDINS: So normally the atmosphere experiences change with night and day. But the eclipse coming across the country in a dark shadow at an average about 1,500 miles per hour is going to set up waves in the atmosphere.
GREENFIELDBOYCE: There'll be temperature changes. All of that will be monitored. Scientists are also sending up harmless but hardy bacteria.
DES JARDINS: It turns out at high altitude, where the balloons are going to be, is an analogy in temperature and pressure to the surface of Mars.
GREENFIELDBOYCE: And during an eclipse, NASA says it's even more Mars-like, so scientists want to test how life reacts to such an alien experience. Nell Greenfieldboyce, NPR News.
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