Aurora over Clouds
Image Credit & Copyright: Daniele Boffelli
Explanation: Auroras usually occur high above the clouds. The
auroral glow is created when fast-moving particles ejected from the Sun impact the
Earth's magnetosphere, from which charged particles spiral along the
Earth's magnetic field to strike atoms and molecules high in the
Earth's atmosphere. An
oxygen atom, for example, will glow in the green light commonly emitted by an
aurora after being energized by such a collision. The lowest part of an
aurora will typically occur at 100 kilometers up, while most clouds usually exist only below about 10 kilometers. The relative heights of clouds and
auroras are shown clearly in the
featured picture from
Dyrholaey,
Iceland. There, a determined astrophotographer withstood
high winds and initially overcast skies in an attempt to capture aurora over a
picturesque lighthouse, only to take, by chance, the featured picture
along the way.
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