Celestial News: 3 galaxies of autumn
For Steamboat Pilot & Today
One of my favorite times of year for sky watching is early fall when the nights are clear and cool but not yet frigid. On moonless autumn evenings, one can almost see to infinity. In fact, the fall sky offers the opportunity to see the two most distant objects visible to the unaided human eye.
About midway between the familiar W-shaped star pattern of Cassiopeia’s Chair and the Great Square of Pegasus, you’ll find a faint wisp of light, like a tiny detached piece of the Milky Way. Charles Messier catalogued this fuzzy patch as the 31st object on his list of comet impersonators in 1764, so we now call it M31.
It was also known for centuries as the Great Andromeda Nebula, when it was thought to be a spinning vortex of hot gas in our Milky Way. But in the 1920s, American astronomer Edwin Hubble determined that Andromeda’s great nebula was no nebula at all — it turned out to be a near perfect twin of our own Milky Way galaxy at the mind-boggling distance of 2.5-million light years. From that distance, even a collection of a hundred billion suns appears in our sky as that faint wisp seen on a clear, dark night.
The discovery that M31 was a whole other galaxy demonstrated that the universe was far larger than we imagined and soon, thousands of other galaxies were confirmed. Andromeda’s galaxy just happens to be the closest and brightest of the distant galaxies visible from the northern hemisphere, literally in our cosmic backyard.
Astronomers now recognize that the Milky Way and the Andromeda Galaxy are the two dominant members of a small cluster of about three dozen galaxies affectionately called the Local Group. Most of the other members are just little guys, so small and faint that just seeing them requires large telescopes or long exposure photography. Many of them orbit our galaxy as tiny satellites, and the same is true for Andromeda.
There is one other large spiral galaxy in the Local Group of galaxies, and it, too, is faintly visible to the unaided eye on exceptionally dark, clear nights. It is Messier’s object number 33, or M33 for short, also called the Pinwheel Galaxy. It is smaller fainter, and, at 3-million light years, more distant than M31 and is proportionately more difficult to see.
As luck would have it, M33 is found only one hand span below Andromeda Galaxy in our fall sky. Consider yourself among the most visually gifted people if you can spot the faint wisp of M33 with the naked eye. I have accomplished it on several occasions, not by looking straight at it, but by using averted vision to focus its image on a more sensitive part of the retina. Of course, binoculars put both M31 and M33 within easy visual grasp and show them as much more than just mists in the night. Both are visible near the star clouds of our own Milky Way Galaxy arching overhead, the third and grandest galaxy of autumn.
For information about astronomy-related events in Steamboat Springs, including public star parties at Colorado Mountain College’s Ball Observatory, contact physics and astronomy instructor Paul McCudden at email@example.com or 970-870-4537 or visit the SKY Club web page at ColoradoMtn.edu/skyclub.
Jimmy Westlake is adjunct professor of physical sciences at Colorado Mountain College and former Ddirector of the Rollins Planetarium at Young Harris College in Georgia and the St. Charles Parish Library Planetarium, in Luling, Louisiana. His “Celestial News” column appears monthly in the Steamboat Pilot & Today newspaper. Check out Westlake’s astrophotography website at JWestlake.com.
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