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Are You Pro or Constellation?

Week of September 27, 1999

If you even glance at the night sky from a dark site, you'll see that stars are not evenly spread out across the heavens. They tend to be in clumps, clusters or patterns. Some places in the sky are loaded with stars, other have only a few.

This is no illusion. Stars do tend to be near other stars. As a matter of fact, clustering happens on all scales in the Universe, from just a few stars hanging out in a small group to vast conglomerations of galaxies hundreds of millions of light years across. Over the next few weeks we'll take a look at these different types of clusters, from smallest to largest.

Okay, I lied. We won't start with the smallest, we'll start with the easiest to see. When you look up in the sky, it's hard not to see patterns formed by stars. No one knows for sure just which civilization first saw patterns in the sky, or even if they predate written history. But anyone who looks up can't help but see familiar shapes in the sky. We call these patterns of stars ``constellations'', meaning ``groups of stars''.

Different people see different shapes, so it's no surprise that different cultures have different names and even boundaries for the constellations. Some are fairly universal, like Orion. To almost everyone, this looks like a man. The stars are so bright and the constellation so easy to see that most cultures figure him as a hero, or at least a larger than life figure. Most constellations have myths and stories about them too, and many of these stories are pretty entertaining. One of my favorites is about a king and a queen who get a young man to cut the head off a gorgon which he uses to save a beautiful princess from a sea monster (this has been done countless times in Hollywood, probably most notably in ``Clash of the Titans''). All these characters are actually constellations: Cepheus, the King; Cassiopeia, the Queen; Perseus, the hero; Andromeda, the Princess; and Cetus, the Sea Monster. Even the gorgon (Medusa) is represented by a star in the constellation of Perseus.

Constellations are just chance alignments of stars as seen by us here on Earth. Stars are actually at all different distances, some brighter, some dimmer. For example, Betelegeuse, the orange star marking Orion's right shoulder (to us, facing him, it's on the left) is about 430 light years away, while Rigel (Orion's left foot) is nearly twice that far! (This has led some people to some Bad Astronomy about constellations too.)

Stars are so far away that from every planet in the solar system they would appear by eye to have the same patterns. Maybe someday, your descendants may stand on the surface of Mars and gaze up into the sky. The patterns they see there will be the wholly the same as those seen by our distant ancestors, when they first became intelligent enough to look up and wonder.

Want to know more about constellations? Try Chris Dolans' extensive and fun constellation website.



©2008 Phil Plait. All Rights Reserved.

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