Winter Stargazing

Orion Takes Center Stage
By Philip Harrington
La Ventana Arch with Orion
La Ventana Arch with Orion (iStockphoto)

For many stargazers, winter is the favorite season, when the smog and haze that mask the heavens give way to crystal-clear nights. Though it is sometimes difficult to face the cold temperatures, the winter sky—glittering with a king's ransom of stellar jewels—makes it all worthwhile.

Standing center stage is Orion, the Hunter, the most brilliant constellation of all. Look for three equally bright stars in a row, which form his belt. To the north lies the bright reddish star Betelgeuse—the right shoulder of the Hunter (seen on our left). His left shoulder (on our right) is represented by the star Bellatrix. Above the shoulders is a faint group of three stars depicting Orion's tiny head. Below the belt are the stars Rigel, representing Orion's left knee, and Saiph, marking his right knee. He is shown holding a shield of faint stars in his left hand, and a club raised high over his head in his right.

Orion is the best constellation for demonstrating that stars come in different colors, and that these colors depend on the stars' temperatures. The Sun is a yellow star and has a surface temperature of about 11,000 degrees F. Compare that to blue-white Rigel, one of the hottest stars known. Rigel's surface temperature is about 23,000 degrees F! At the other end of the scale is red Betelgeuse. Its surface temperature is only about 5,000 degrees F.

Hanging from the belt of Orion are the dim stars of his sword. The middle star in the sword is not actually a star at all, but rather a cloud of glowing hydrogen gas called a nebula. Astronomers have cataloged it as simply "M42," but most backyard stargazers know it better as the Great Orion Nebula. The Orion Nebula is visible through all binoculars and is a wonder to behold through telescopes. Deep within, hundreds of stars are forming from the clouds that make up this celestial nursery.

Orion's Place in Mythology
According to one legend, Orion was the mightiest hunter of all time. One day, he boasted of being able to defeat any animal on earth. His constant bragging was overheard by Mother Earth, who, fearing that he would destroy every creature, sent a poisonous scorpion to sting Orion on the heel and kill him. But Diana, goddess of the hunt, felt sorry for Orion. To honor him, she placed Orion among the stars. (The scorpion, Scorpius, was also placed in the sky. It may be found under heavy guard in the summer sky, directly opposite Orion so that it would never harm him again.)

Supergiant Star
Though we might not suspect it just by looking, Betelgeuse is one of the largest known stars. Classified as a red supergiant star, it measures about 640 million miles in diameter—more than 700 times larger than our Sun. Put another way, if Betelgeuse were at the center of our solar system, its outer edge would extend beyond the orbit of Mars! (Mars, the next planet after Earth, is more than 141 million miles from the Sun. Earth, at 93 million miles out, would be inside the star!)

Article (C) Philip Harrington, 2000. An ardent amateur astronomer and author, Philip Harrington is a former staff member of New York City's Hayden Planetarium and instructor at the Vanderbilt Planetarium. He currently teaches astronomy courses at Suffolk County Community College.


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