Western Slope Skies - The Color of Stars
For astronomers, it’s not all black and white…
At first glance, our night skies can appear as a dark canvas illuminated with points of mono-hued light. But, as your eyes adapt, and on closer inspection, one can pick out stars with colors that are blue, white, gold, and reddish orange.
Stars are hot, dense balls of ionized gases called plasma. Their color relates to the temperature of the glowing plasma at their surfaces. The hottest stars have surface temperatures of around 35,000 deg F. They shine with a blue-white light. The coolest stars have surface temperatures of about 8000 deg F, and they appear reddish. Gold, yellow, and white stars, like the sun, have intermediate surface temperatures.
Of course, color is sometimes more than meets the eye. At public events we are often asked why bright stars low on the horizon appear to sparkle in different colors. This sparkling does not originate in the stars, but is caused by earth’s atmosphere dispersing the starlight, much like a prism disperses sunlight. When a star is higher in the sky, especially when viewed through a telescope, its color can be distinct.
During January evenings, we can see some very colorful stars. With the un-aided eye, the winter constellation Orion, The Hunter, contains some beautifully colored stars, especially reddish Betelgeuse at Orion’s left shoulder and the contrasting blue-white Rigel at his right foot. Northwest of Orion, you’ll find the bright star, Aldebaran, signifying the fiery red eye of Taurus, the bull. Southeast of Orion gleams blue-white Sirius, the brightest star in the night sky.
Van Gogh envisioned a colorful “Starry Night” in his famous painting, and if you brave the cold and dark for a short time, you can too.
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written & recorded by Joyce Tanihara.