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Absolute Beginners - Winter Skies
Many bright stars sparkle on crisp winter evenings. Best of them all is Sirius, the brightest star in the entire sky. Sirius is popularly known as the Dog Star, as it marks the face of one of the dogs of Orion the hunter.
Sirius is a white star, but as seen from mid-northern latitudes and above – say, the northern US, Canada and Europe – it twinkles many colors. This is because its light is split up by air currents in the Earth's atmosphere when it lies close to the southern horizon. From the southern US it lies higher up in the sky and does not twinkle so much. Because of the twinkling, it is often mistaken for a spinning UFO. (For more information on this effect, follow the link below to "How to Tell a Planet from a UFO.")
Sirius is part of the constellation Canis Major, the larger of Orion's two dogs. Orion has a second, smaller dog, represented by the constellation Canis Minor. The brightest star of the smaller dog is Procyon.
Those in the southernmost states of the US will also be able to see the second-brightest star of all, Canopus. It huddles low on the southern horizon on winter evenings, almost due south of Sirius. Canopus was part of the ancient Greek constellation of Argo Navis, the ship of the argonauts, in which it marked the ship's steering oar. Canopus was named after the navigator who worked for the Greek King Menelaus. Fittingly, Canopus is now used as a navigation star by space probes.
Above and to the right of Sirius is the constellation of Orion, the giant hunter. His most distinctive feature is his belt, formed by a line of three moderately bright stars. They just fit into the field of view of normal binoculars. Beneath the belt lies his sword, where you will find a hazy patch that is the Orion Nebula, a giant cloud of glowing gas where new stars are being born. You can detect it with the unaided eye but binoculars show it better.
Marking the right shoulder of Orion is the red supergiant star called Betelgeuse, commonly pronounced "Beetlejuice." Betelgeuse, Sirius and Procyon form a striking triangle of stars. By contrast with the ruddy hue of Betelgeuse, Orion's left foot is marked by a blue supergiant called Rigel (pronounced "rye-jell"). Can you see the color difference?
Above left of Orion, if you are looking from the northern hemisphere, lie the stars Castor and Pollux. These mark the heads of the mythological twins of the same name, commemorated by the constellation Gemini. Pollux is, by a small margin, the brighter of the two, and appears slightly orange when seen through binoculars. Castor is blue-white. A small telescope with a sufficiently strong magnification should show that Castor is in fact a double star, although to the naked eye it appears as one.
Now look above right of Orion. Here you will find another famous constellation: Taurus, the bull. Its face is marked by the V-shaped star cluster called the Hyades. This is such a large grouping, as wide as ten full Moons, that even the wide field of view of binoculars can barely encompass it. An even prettier cluster is the Pleiades, appearing as a hazy swarm above the bull's back. Although popularly termed the Seven Sisters, you will need sharp eyes to see more than its six brightest members. Binoculars and small telescopes show dozens more stars in the cluster, splashed over three Moon diameters of sky.
To complete this tour of the winter sky, look overhead (to avoid getting a crick in your neck, it's more comfortable to recline in a lawn chair). There you will find the constellation Auriga, representing an ancient Greek charioteer. Its brightest star is Capella, the most northerly of the first-magnitude stars. For some reason unexplained by mythology, Capella represents a mother goat that the charioteer has tucked under his arm. Two fainter stars nearby, Zeta and Eta Aurigae, represent the goat's kids, also traveling with the charioteer. Is he perhaps planning goat stew?
The Monthly Sky Guide, by Ian Ridpath and Wil Tirion
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