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Moon and Jupiter

December 18, 2013

Stars are giant nuclear reactors. Gravity squeezes them so tightly that their cores heat up to tens of millions of degrees. At such temperatures, atoms zip around so fast that they ram into each other and stick together. That “fusion” process creates heavier elements, while releasing an enormous amount of energy.

A century ago, though, astronomers didn’t know about the fusion part of the process. Instead, one leading theory said the stars shined only because of the first part of the process — the gravitational contraction that heats their cores.

That process does power the hearts of giant planets. The best example is Jupiter, the largest planet in the solar system. Gravitational contraction generates a tremendous amount of heat. That energy radiates through the planet’s layers of gas and out into space. In fact, Jupiter radiates more than twice as much energy into space as it receives from the Sun.

But there’s not enough heat to make Jupiter shine in the visible part of the spectrum, as a star does. Instead, it shines in the infrared, which is visible to special detectors. Indeed, Jupiter is one of the brightest infrared objects in the sky.

Jupiter does shine brightly at visible wavelengths, but it’s light reflected from the Sun, not generated by the planet itself. And you can see just how bright Jupiter is tonight. It looks like a brilliant star to the left or upper left of the Moon as they climb into good view this evening.


Script by Damond Benningfield, Copyright 2013

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