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Tuesday, November 20 , 2018, 3:59 am | Fog/Mist 47º


Dennis Mammana: Well, That’s a Star of a Different Color!

Take a look at colorful Orion after dark. Click to view larger
Take a look at colorful Orion after dark. (Creators.com illustration)

I’ve been gazing skyward for more than five decades, and in that time I’ve learned a few things. One is that novice stargazers have some deeply ingrained misconceptions about the heavens.

For example, many think that we cannot see the moon during the daytime. Others believe that the Big Dipper is always visible in our sky. Still, others think we see the stars as they appear now, rather than as they were centuries ago.

But one of the most common misconceptions is that if you’ve seen one star, you’ve seen ’em all. This is a pretty understandable perspective. After all, stars appear simply as points of light. How different could they possibly be?

Well, ask any experienced sky watcher and they’ll tell you that no two stars are exactly alike — each displays its own personality in a number of ways. I like to say that stars are people, too.

One of the most visible characteristics of a star is its color. Most stargazers don’t notice this immediately because the human eye is not capable of perceiving color well under low light conditions.

You know this to be true if you’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 you find that you’re surrounded by vibrant colors.

When gazing skyward, we discover that star colors are quite subtle. Binoculars or telescopes capture much more light than the human eye and make the colors a bit more obvious. So, if we’d like to see star colors with the naked eye, we need to look toward the brightest stars.

The best place to start your search is within the great constellation of Orion, the hunter. Look for it midway up in the eastern sky after dark this time of year.

We can trace the four bright stars of Orion’s large vertical rectangle, which form the hunter’s shoulders and knees. At its center lie three stars that form a nearly straight line, the belt of the great hunter.

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

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 F) and can often live much longer than the sun.

Bluish-white stars like Rigel, on the other hand, are tremendously hot (18,000 F); they can only burn that furiously for a relatively short time and therefore are much younger than the sun.

After you’ve noticed these two fine examples of stellar color, check out some of the other bright stars around the sky to see what you can learn about their relative temperatures and ages. Once you do this you’ll begin to realize that stars are not all the same.

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. The opinions expressed are his own.

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