Sky watch: What colors tell us about stellar temperatures

Beginning stargazers often have some deeply ingrained misconceptions. One of the most common is this: "If you've seen one star, you've seen 'em all."

Experienced sky watchers, however, know that no two stars are exactly alike. Each can display its own personality in a number of ways, but often the most visible is a star's color.

Most people don't notice this immediately because the human eye isn't capable of perceiving color well under low-light conditions. We know this to be true if we've ever looked around a relatively dark room; shapes and shades of gray are pretty easy to spot, but colors are virtually nonexistent. Turn the lights on, however, and we see we're surrounded by vibrant colors.

When gazing skyward, we discover that star colors are quite subtle. Binoculars or telescopes help, but if we'd like to see star colors with the naked eye, we need to look toward the brightest of stars.

The best place to start is within the constellation of Orion, the hunter. At this time of year, Orion stands majestically midway up in the southern sky after dark. Its large vertical rectangle of four bright stars forms the hunter's shoulders and knees; at its center lie three stars that form a nearly straight line - Orion's belt.

The bright star marking the northeastern corner (the shoulder) of Orion is known as Betelgeuse. This red supergiant glows with an orange light that is pretty tough to miss. At the opposite corner (in the hunter's knee) lies sparkling Rigel, a supergiant that glows slightly bluish-white.

Star colors are more than just a curiosity; they tell us something about stellar temperatures. While our sun glows with a surface temperature of around 10,000 degrees Fahrenheit, reddish-orange stars like Betelgeuse are relatively cool (6,300 degrees) and can live much longer than the sun. Bluish-white stars like Rigel, on the other hand, are tremendously hot (18,000 degrees); they can burn this furiously for only a relatively short time and, therefore, must be much younger than the sun.

Check out some of the other bright stars to see what you can learn about their temperatures and ages.