Autumn: falling leaves lay bare the Great Andromeda galaxy, our nearest spiral-galaxy neighbor.
The Milky Way and Andromeda galaxies are both spirals, notable for their winding arms of bright, young stars and nebulae. M31 is tilted almost edge-on to our line of sight, so we see it as a highly elongated oval instead of a round disk with clearly defined arms.
Despite M31's large distance-2 1/2 million light-years--its hazy glow is visible to the unaided eye in a moderately dark sky. Starting with the Great Square of Pegasus on our all-sky maps, move leftward to the star Beta ([beta]) Andromedae, or Mirach. See also the chart below. Draw a line from Mirach to Mu ([mu]) and the same distance beyond. If you're unable to spot the galaxy with your eyes alone, a pair of binoculars should show an oval mist that grows brighter toward its center.
Through a 4-inch telescope at a magnification of 20x, M31 bridges most of the field of view when observed in a truly dark sky, and at 50x it extends beyond the field! This big eerie glow harbors a small, round, bright inner core enveloped by an oval outer core that fades gently toward its edges. At the galaxy's very heart is an elusive, almost starlike nucleus.
Large galaxies generally have a retinue of dwarf galaxies orbiting them, and the Andromeda Galaxy shows two in the same low-power field. The brighter one is M32, found at the edge of its parent galaxy south of its nucleus. Under moderately dark skies M32 is bright enough to be seen through binoculars, but it's very tiny and looks like a fuzzy star. A 4-inch telescope at 50x shows a small, round, bright spot that grows brighter toward its stellar nucleus.
The other is M110, much fainter, off the opposite side of M31 from M32. It's a filmy oval mist half again wider and three times longer than M32. It's hard to see at all if your sky suffers significant light pollution.
Within the Andromeda Galaxy dwells an association of super-luminous stars designated NGC 206--a challenging target for a novice stargazer, but faintly visible in a 4-inch scope under dark skies. NGC 206 makes a squat triangle with M32 and the nucleus of M31, but the trick is to keep these distractingly bright objects out of the field of view. At 90x NGC 206 is a faint oblong haze approximately as long as M32 but a third as wide. It's one of the largest stellar associations in our Local Group of galaxies, and astronomically speaking it's quite youthful--a mere 20 million years of age.
What about M31's spiral arms? They can be seen, but perhaps not quite as you'd expect. The flank of the galaxy facing M32 fades gradually into the background, whereas the opposite side seems to end rather abruptly. That abrupt drop in brightness marks the position of a dark dust lane between two of the spiral arms on the galaxy's near side. It's the inner dark arc upper right of the core in the photo above. If the sky is very dark and transparent, a 4-inch scope at 50x can show a band of faint fuzz beyond this dark lane--the next spiral arm outward. A 10-inch scope may show another dark lane beyond this followed by an even dimmer spiral arm.
On the opposite side of bright Mirach from M31 lies another nearby spiral galaxy, M33. It's smaller, quite a bit dimmer, and more of a challenge in binoculars.
Go back to Mirach and take a closer, telescopic look. Through a 4-inch scope at 70x, orangish Mirach is accompanied by the small round glow of the galaxy NGC 404, affectionately called Mirach's Ghost. The glare from Mirach may hinder your efforts to spot the galaxy. If so, try placing Mirach just outside the southeastern edge of your field of view. NGC 404 is 0.1[degrees] north-northwest of Mirach, approximately on a line from Mirach to Mu.
Now let's visit Almach, the end star in Andromeda's arc. It's one of the prettiest double stars in the sky! At 90x a 4-inch scope reveals a bright, beautiful golden primary escorting a fainter companion with an icy blue-white tint. The companion is actually composed of three stars, all currently too close together to be separated through a backyard telescope.
Also, look for the star marked Upsilon ([upsilon]) on our chart. Upsilon and Almach make a nearly equal-sided triangle with the lovely star cluster NGC 752 to their south. In 10x50 binoculars, you can see about 15 of this cluster's stars in a suburban sky and twice as many in a rural sky. A hockey stick of little stars stands next to NGC 752, its handle to the west and the business end whacking the southern part of the cluster. In a 4-inch scope at 40x, NGC 752 sports dozens of stars and nearly fills the field of view, as in the photo on the facing page--a worthy pile of jewels with which to close our autumn tour.
Sue French is a long-time SkyWatch contributor and a renowned deep-sky observer. Her widely acclaimed book Deep-Sky Wonders is available at ShopatSky.com. She welcomes your questions and comments at scfrench@ nycap.rr.com.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||Observing: Deep-Sky Delights|
|Date:||Jan 1, 2014|
|Previous Article:||Summer: hot summer days mean the milky way arching high at night.|
|Next Article:||Get the eight telescope: every year countless people buy their first telescope--but too few of them know what to look for.|