Wednesday, December 06, 2006

More spectra

So, remember yesterday I said that the fingerprints of the elements that make up a star are visible in its spectrum. But what about the spectra of things in our solar system? Planets and moons don't make their own light, they just reflect sunlight. So you should expect the reflected light to have a spectrum identical to the sun.

For the most part, this is true. Below are three spectra. The first is of the sun, the second is of Saturn's moon Titan, and the third is of the planet Uranus. You can click on an image for a larger view.

Notice that Titan (the middle spectrum) looks a lot like the sun, with the exception of a little less blue light and a band of red light that is ever-so-slightly diminished. If you look at a color picture of Titan, you can see that it is yellowish -- the same color as the sun, but with less blue light.

The spectrum of Uranus, on the other hand, looks much different from the sun. Some colors are completely missing, and there is almost no red light! You are still seeing the spectrum of the sun, but the atmosphere of Uranus (mostly methane) has absorbed those "missing" colors of light. Once again, if you look at a color picture of Uranus, you'll see it is a greenish blue, the same as the colors of light left in its spectrum.

Tomorrow I'll finish up showing off my spectra with a few objects from outside the solar system.

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