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| For education orders please call 1-877-290-8256. Welcome to the October Third Week Featured Article! Spot the Andromeda Galaxy Geoff Gaherty, Starry Night EducationAutumn is the best season of the year for astronomical observing. The bugs of summer are gone, winter’s cold has not set in, and it gets dark at a reasonable hour. For most amateur astronomers, our favourite targets are what we call "deep sky objects." By this we mean large structures beyond the stars in our immediate neighborhood in the Milky Way Galaxy. They include clusters of stars within the Milky Way and galaxies, distant islands of stars. Because of their distance, these objects are faint and hard to see. You may need to travel to a darker location to see them. Amateur astronomers usually locate objects in the sky with a technique called "star-hopping." This uses the brighter nearby stars to locate the fainter more distant objects. 
Use the autumn constellation patterns to locate the Andromeda Galaxy and other deep sky objects. Credit: Starry Night software. The chart shows the eastern sky as it appears around 8 p.m. in late October. The first thing that you’ll notice is that there are no bright stars. That’s because at this time of the year we are looking northward out of the disk of our Galaxy, so there are relatively few stars to interfere with our view. The brightest star in this chart is Mirfak in the constellation Perseus, just barely above second magnitude. There are many stars just under second magnitude, which form several easily recognized patterns, which we call constellations. Front and central, about halfway towards the zenith, is the Great Square of Pegasus, tilted over by 45 degrees. This will look larger in the sky than it does on the chart; take that into account when looking for it. Off to the left of Pegasus is the "W" shape of Cassiopeia. Below it is Perseus, one of the richest areas in our Milky Way Galaxy. Pegasus, Cassiopeia, and Perseus form the skeleton of stars, through which we will look for more distant targets. First and foremost is the Andromeda Galaxy: the largest galaxy in the group which includes our Milky Way, located 2.54 million light years distant. That means that the light we see from its trillion stars has been traveling towards us for over two million years. Beginning stargazers often get confused over objects named after the constellation they are found in. Thus "Andromeda" can refer to both the Andromeda Galaxy, and the constellation Andromeda, in which it is found. Similarly, "Milky Way" can refer to both the galaxy in which we live, and the band of its distant stars which we see in our night sky. The Andromeda Galaxy is most easily located by using the constellation Cassiopeia as a guide. If you think of the right-hand part of the "W" as an arrow head, it points directly towards the location of the Andromeda Galaxy. A more precise way to locate it is to start with the Great Square of Pegasus. Its leftmost star, Alpheratz, marks the head of the Andromeda, the queen of Ethiopia in Greek mythology. Andromeda itself consists of two streams of stars forming pairs. Find the second pair to the left of Alpheratz, and then project these upwards. This will take you right to the Galaxy. What should you look for? Andromeda is so far away that its trillion stars combine to make a very faint glowing patch. This is most easily seen in binoculars, but once you spot it in binoculars, if you have a dark sky, you should be able to see it with your unaided eye. I live in the country, and can see Andromeda any clear moonless night, but, when I lived in the city, I could only see it with binoculars. People seeing Andromeda for the first time will swear it is the faintest thing they have ever seen, though to experienced astronomers it seems blindingly bright. A useful trick for teasing it out of the background is to use what astronomers call "averted vision." This takes advantage of a feature of the human eye where our most sensitive vision is just slightly away from the centre of our field of vision. So look slightly off to one side of Andromeda’s location, and it should pop into view. It is actually easier to see Andromeda in binoculars than in a telescope because it is so large. It is larger than the field of view of most telescopes, so it’s easy to sweep right over it without noticing it. Use the lowest magnification and widest field of view available on your telescope. While looking at Andromeda, see if you can see its two satellite galaxies. These will appear farther away than they look in photographs, because photographs are made with long exposure times to record the outer reaches of the galaxy, making it appear much larger than it does in telescopes or binoculars. One satellite, Messier 32, is quite easy to see, being almost as bright as the main galaxy. The other satellite, Messier 110, is more of a challenge because it has a low surface brightness. Now for some easier targets. These are clusters of stars within our own galaxy. The brightest is known as the Pleiades, or the Seven Sisters. In the early evening it is down low close to the horizon; by 3 a.m. it is almost overhead. This is easily seen with the unaided eye, even in the city. Without any optical aid, you can spot about six stars in this cluster, but binoculars will reveal dozens more. In Japanese this cluster is known as Subaru, and the automobile named for it uses its stars as their logo. The Pleiades are located 410 light years from the Sun. Between Cassiopeia and Perseus is a pair of star clusters, known as the Perseus Double Cluster. This is a treat in binoculars or a small telescope, consisting of hundreds of stars densely packed together. They are located 7 and 8 thousand light years away. The final object is much more challenging: the Triangulum or Pinwheel Galaxy. You can find it using the same two stars we used to find the Andromeda Galaxy, but going in the opposite direction, south instead of north. It is 2.87 million light years away, slightly farther than Andromeda. Though easy enough to find, Triangulum is very difficult to see. Although large in size, larger than the Full Moon, and quite bright, it has a very low surface brightness because of its size and orientation. We see it in "plan view," so that its outer reaches fade away into nothingness without any sharp edge to catch our eye. Seeing Triangulum requires a dark sky and either binoculars or a telescope with a wide field of view. Despite the difficulty, some sharp eyed observers have actually spotted it without any optical aid. In fact, it is used as a marker of an extremely dark sky and extremely sensitive vision. |
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