One of the great icons of our times is the word “galaxy,” which appears in the news media and on the Internet almost daily. Most of these majestic denizens of deep space require a telescope to be seen since they lie many millions and even billions of light-years away. But there’s at least one that requires no optical aid to see, being strikingly visible to the unaided eye on a dark clear night — and that’s the galaxy we live in! We’re referring, of course, to the Milky Way.
Nightfall on September evenings finds our Galaxy at its shimmering best. Flowing all the way from the northeastern horizon to the southwestern one, and passing dramatically right overhead, it spans an amazing 180 degrees of the sky. (Galaxies typically viewed through a telescope look much smaller than the apparent size of the full Moon, which is only about _ degree across at its average distance.) Since we’re living inside this giant starry pinwheel, it actually encircles the heavens. The other half crosses the winter sky from horizon to horizon as well, but it’s less striking since we’re then looking out towards the “thin” side of the Milky Way to its edge. In summer, we’re facing into the bulbous center of the Galaxy, whose hub is located in Sagittarius (see below).
One of the brightest sections of the Milky Way can be seen by finding the Summer Triangle asterism (see October’s Sky Talk for more about asterisms). Positioned high overhead these nights, it’s formed by the radiant blue-white stars Vega in Lyra, Deneb in Cygnus, and Altair in Aquila. The Summer Triangle itself can be seen even under the brightest of city lights, so it’s readily identified. Using it as a starry marker, seek a dark (preferably Moonless) night away from intruding lighting and you will behold the Milky Way in all its glory!
Even more striking is the huge glowing mass of stars billowing out of and upward from Sagittarius, which is marked by another easily-recognized asterism — that of the Teapot. So bright is the Galaxy here that it’s not uncommon for people seeing it to think that rain clouds are forming. But these are actually starclouds! Sweeping along the course of the Milky Way with Edmund binoculars at this time of year on a dark, transparent night — especially in those areas of the Teapot and the Summer Triangle — is an exhilarating experience never to be forgotten.
While doing so, you should be aware of an amazing illusion that can occur at anytime without warning. It can be experienced using wide-angle binoculars and even with no optical aid at all. (The effect isn’t visible in telescopes themselves due to their relatively small fields of view and also the fact that you need to use both eyes to see it.) As you gaze at one of the Galaxy’s massed starclouds and realize that the brighter stars you’re seeing are closer to you than are the fainter ones — that you’re actually viewing layer upon layer of stars and thus sensing “depth” — the Milky Way may suddenly jump right out of the sky at you as the vast starry pinwheel it is!
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Guest post: This article originally appeared on the Edmund Scientific site, as part of their Sky Talk series. The article was written by James Mullaney, former assistant editor at Sky & Telescope and author of five books on stargazing. Edmund Scientific has graciously agreed to let us post these articles to provide additional resources for Earth Science and Astronomy educators.
