Sky Talk August 2011: The Great White Way

New York City’s famed “Great White Way” is not the only thoroughfare to be so named. There’s a far richer and vaster one visible from anywhere on the planet — and it’s found in the Summer sky! We’re referring to the Milky Way, the grand thoroughfare of our home Galaxy. And August is one of the best times of the year to see and experience its magnificence.

Most readers know that we’re living in a vast spiral galaxy called 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 regions, while in Winter we’re facing the opposite direction and seeing its thin outer portions — with the result that our Galaxy is much less obvious and striking during that season. (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 Great White Way of our Galaxy at its best, begin by setting your Scientifics Star and Planet Locator to the date and time you decide to head outdoors — preferably on a dark (moonless) and exceptionally clear night. Avoid sources of bright illumination such as porch and street lights, and 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 brighter constellations shown your Locator (and a red light to maintain your dark-adaptation while doing so). Note how the pale path of the Milky Way shown on the rotating chart stretches from the northeastern horizon all the way across the sky to the southern one, passing nearly overhead in August. Now compare this to the real sky, especially where its rich starstream courses through Cygnus, Aquila, Scutum, Scorpius — and especially in the direction of the Galaxy’s center in Sagittarius, where its big billowy starclouds are so intense that many actually mistake them for rainclouds forming!

Taking your exploration a step further, next turn your Edmund binoculars or Astroscan wide-field telescope skyward (using the latter’s low-power 16x eyepiece). Sweep along the entire course of the Milky Way from horizon to horizon. The Galaxy will suddenly come alive with beautifully-tinted stars, glittering clusters and misty-looking nebulosities. You will then fully sense the awesome majesty of our Galaxy in all of its glory!

A final word about August’s sky: the annual Perseid Meteor Shower will be a total wash-out this month due to the Full Moon occurring on the same night as its peak activity. (This is in stark contrast to what occurred last year at this time — see the August 2010 installment of Sky Talk!)

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