Sky Talk January 2008: The Winter Milky Way

Mention of the Milky Way conjures up images of Summer nights, at which time the great billowy starclouds of our home Galaxy provide an awesome sight as they pass through the rich constellations of Cygnus, Aquila, Scutum, Scorpius and, especially, Sagittarius which lies in the direction of the Galaxy’s center. But there is a Winter Milky Way as well — and January is a great time to view it!

Most readers know that we’re living in a vast spiral galaxy known as the Milky Way. Some 100,000 light-years across, it’s about 15,000 light-years thick at its central hub and tapers off to as little as 5,000 light-years at its very edge. We’re located about two-thirds of the way out from its center located in the direction of the constellation Sagittarius. On Summer nights we are looking into its thickest and riches part, while in Winter we’re facing the opposite direction and seeing its thin outer portion. As a result, during the latter season the Milky Way is much less obvious and striking than during the former. But it’s still there! (In Spring and Fall, the Milky Way lies along the horizon and we look out at right angles to its long dimension into intergalactic space itself.)

To view the Winter Milky Way, begin by setting your Scientifics Star and Planet Locator to the date and time you go outdoors — say 9:00 p.m. on January 15th. Note how the pale star stream of the Galaxy shown on the rotating chart stretches from the northwestern horizon to the southeastern one, passing nearly overhead. Along its way, it courses through the well-known constellations Cepheus, Cassiopeia, Perseus and Auriga, and then skims across the borders of Taurus, Gemini and Orion, finally flowing into Monocerotis and Puppis.

Now wait for a dark (moonless), clear transparent night and go outdoors. Avoiding sources of bright illumination such as porch and street lights, give your eyes time to adjust to the night by remaining in darkness for 10 to 15 minutes. Use this time to identify the starry outlines of the constellations just mentioned with your Locator (and a red light to maintain your dark-adaptation while you do). Now look at the path of the Milky Way on the chart and compare it to the actual sky. You will then behold the pale glow of our Galaxy, especially where it passes overhead and is at its brightest.

Taking this a step further, next turn your Edmund binoculars skyward. Sweep along the entire course of the Milky Way from horizon to horizon. The Galaxy will suddenly come alive with glittering tinted stars and misty-looking clusters — actual stellar communes or families of distant suns! One of its most magnificent sections will be found high overhead near the center of Perseus. It’s known as the “Alpha Persei Association” for the constellation’s brightest star, from which a stream of glittering blue-white diamonds will be seen trickling southward. And while the Winter Milky Way can’t compare to its radiant Summer counterpart for most stargazers, it has a special charm and character all its own for those who would brave cold wintry nights to explore it.

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of five books on stargazing.

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