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The aurora borealis, or northern lights, is usually a calm band of greenish light in the sky. But occasionally, plasma ejected from the sun causes magnetic storms in space, and those storms release bursts of energy called substorms -- the same way that thunderstorms spin off tornadoes. Substorms make the aurora expand and "dance" across the sky, but they are also are accompanied by radiation that can endanger communications satellites and even astronauts, so researchers want to know more about how and where they start. Vassilis Angelopoulos, the principal investigator of NASA's THEMIS (Time History of Events and Macroscale Interactions During Substorms) mission and a research physicist at the University of California, Berkeley, explains how THEMIS will investigate substorm triggers.
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The sun emits a stream of charged particles -- mostly high-energy electrons and protons -- called the solar wind. |
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The Earth's magnetic field is similar to that of a bar magnet, with a north and a south pole. |
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The solar wind distorts the Earth's magnetic field -- also called the magnetosphere -- by pulling it out into a long tail on the side of Earth that faces away from the sun. Eventually the magnetic field lines get stretched too far and snap back, causing magnetic substorms. |
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NASA has placed five satellites in the region of Earth's stretched-out magnetosphere. The satellites will measure magnetic currents at those locations to learn more about how and where substorms start. |
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Substorms cause the aurora borealis -- the northern lights -- to light up, move and "dance" in the sky. |
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Ground-based observatories that include fish-eye cameras to take pictures of the aurora, as well as magnetometers, will help researchers pinpoint where and when substorms occur. |
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The ground-based observatories are located throughout Canada and the Northern United States. Red dots indicate full ground-based observatories; blue dots indicate magnetometers placed at rural schools as part of the project's education outreach component. |
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The observatories will each capture a portion of the sky above the United States and Canada. Together, they will provide footage of the entire night sky. |
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Ground-based observatories will photograph the aurora borealis in the night sky. |
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