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Moon and Aldebaran

October 25, 2010

The bright "eye" of Taurus, the bull, winks up at the Moon tonight. Aldebaran is to the lower right of the Moon as it rises around 9 o'clock, and to the lower left of the Moon at first light tomorrow.

Over the decades, astronomers have compiled a lengthy dossier on Aldebaran. They have accurate measurements of its distance, size, and brightness. They also know its temperature, and they know a good bit about its composition.

Much of this information comes from a technique called spectroscopy. An instrument attached to a telescope splits the star's light into its individual wavelengths or colors, known as a spectrum. Chemical elements in the star itself, or in the cooler gas that forms the star's atmosphere, leave their own "fingerprints" in the spectrum.

From Aldebaran's spectrum, astronomers know that the star contains fairly low amounts of metals, like iron. In fact, the percentage of iron in Aldebaran is only about half that of the Sun.

Spectroscopy also reveals a star's surface temperature. Aldebaran is more than 3,000 degrees Fahrenheit cooler than the Sun is. Cooler stars look redder than hotter ones, so Aldebaran shines with a distinctly orange color -- something that you don't need sensitive scientific instruments to see -- it's easily visible to the naked eye.

We'll have more about Aldebaran tomorrow. In the meantime, look for this bright orange star following the Moon throughout the night.


Script by Damond Benningfield, Copyright 2010


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