The Sun's Hot Atmosphere

PureInsight | January 2, 2001

Hold your hands near a campfire -- in its 'atmosphere,' we'll say -- and they get warm. The closer you get, the warmer it is. If you stick your hands in the fire (and we don't recommend it) you would find it even hotter.

Likewise, you might expect the Sun to be hottest in the middle, and then get cooler as you moved to the surface and then farther out. But, in fact, the temperature rises sharply in the Sun's atmosphere, called the corona. And the same is true of other stars.

Weird, because there is a law that says this can't be so.

'The second law of thermodynamics says that temperature can only drop when you move away from the heat source,' says Markus Aschwanden, a solar researcher at the Lockheed Martin Solar and Astrophysics Laboratory. 'So there is something magic and invisible that heats the solar and stellar coronae.'

After many decades of research into this weird thing, scientists are only beginning to understand what might be going on.

(Image: Ultraviolet-light image of coronal loops, large arcs of gas and energetic particles that make up the Sun's corona, as seen by the TRACE satellite telescope. )

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