The constellation of Orion and its neighbors contain what is called the Winter Circle of Stars. Look on any star chart and find Orion, Canis Major, Canis Minor, Gemini, Auriga and Taurus, circling westward as winter ends. These six constellations contain a visible "circle" of very bright and colorful stars. If you can imagine the circle as a clock, we'll begin with Capella, yellow like our sun in the one o'clock position. Capella is the bright yellow star in the constellation Auriga, found above the shoulders of Orion. Red Aldebaran, the eye of the bull Taurus is at the three o'clock position. Red stars are the oldest and coolest. At five o'clock, stands Rigel, the brilliant blue knee of Orion, the hunter. Rigel is young and very hot! Diamond white Sirius, the brightest star in the sky, is below Orion in the constellation Canis Major, the great dog. It fills the seven o'clock position. At nine o'clock is Procyon, another yellow star like our sun, in the constellation Canis Minor. The Gemini Twins, Castor and Pollux complete the circle at eleven o'clock. Castor is white and Pollux (the brighter of the twins) is red. Within the circle are red Betelgeuse, the shoulder of Orion, and blue/purple stars Alnitak and Mintaka, the pretty belt stars of the constellation Orion.
Through a spectroscope these stars give away many secrets. The observer sees the color spread out in a bar shaped spectrograph. The bar is broken into the colors of the rainbow, purple at one end and moving through the spectrum of blue, green, yellow, orange and red. The observer can take the temperature of the star, and tell you its age from the information on the spectrogram! Bars of shadow called absorption lines and bars of concentrated illumination called emission lines are the main indicators of age and temperature.
That's a pretty interesting observation to share at a star party!
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