Careful observation of the sky reveals that the colors of stars are not all the same. Their jewel-toned hues are easier to spot on long-exposure photographs, but it is also possible to see these colors with your own eyes. The color of a star is related to its temperature. At one end of the spectrum are blue stars, which are young and hot, in the middle are yellow and white stars of moderate age and temperature, such as the sun, and finally are the red, cooler stars nearing the ends of their lives.The following stars can all be seen at the same time about two hours after sunset this weekend. To help determine what color your eyes see, compare the stars to each other with just your eyes, a pair of binoculars, or a telescope.
Stars that might look blue to you are Rigel, Spica, and Vega. White stars include Capella and Sirius. Arcturus and Aldebaran should have an orangey glow, and Betelgeuse will appear more reddish in color.
The star Rigel in Orion will quickly set in the west, so it’s probably the first star you want to look for. It marks the left “knee” or “foot” of Orion the Hunter. Compare this blue star to the orange and red stars nearby. Red Betelgeuse is in the opposite corner of Orion, marking the hunter’s right shoulder. Rigel is the brightest star in Orion and Betelgeuse is second brightest. To Orion’s upper right is the V-shape of Taurus and its brightest star, Aldebaran. Can you see a color difference between red Betelgeuse and orange Aldebaran?
Another contrasting pair, orange Arcturus in Bootes and blue Spica in Virgo, are easy to find. These two bright stars lie in the east-southeast, with Spica closer to the horizon and Arcturus above it. A clever device to help remember where they are is to follow the curve off the Big Dipper’s handle and “arc to Arcturus and speed on down to Spica.”
Look at the northeastern horizon to find Vega rising. Does it look blue or white to you? As it rises higher from the horizon and out of the thick layers of atmosphere, does it appear to change color? The last two stars are white stars, although one may look yellow-white while the other might appear more blue-white. The stars, Sirius and Capella, are positioned on either side of Orion. Sirius in Canis Major is the brightest star in the sky and can be found low on the horizon in the west. Then trace a line past Betelgeuse (Orion’s shoulder star) to find bright Capella in Auriga higher in the northwest. Which of these white stars looks more yellow to you and which looks more blue?
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Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She is currently the Feature Writer for Astronomy and Space at Suite101.com. You can follow her on Twitter at twitter.com