How much can you see of the Andromeda Galaxy system with just a pair of binoculars? Turns out a lot!
Only tiny increases in aperture and magnification are needed to open new cosmic vistas never dreamed of by ancient skywatchers: Moon craters, Uranus and Neptune, tens of thousands of unseen stars, even asteroids. All these with nothing more than a pair of 7x50 binoculars.
This classic glass and similar models—8x40, 7x35 and 10x50—will serve you well on part two of our journey to the Andromeda Galaxy we began last week with our naked eyeballs. Using binoculars does take a bit of practice: first you have to focus them. Sounds simple, but many beginners struggle with the task.
First, set the eyepiece spacing. Grasp the barrels of the binoculars and either pull them apart or squeeze them together until the images seen through the barrels form a single, circular field of view. Now, close your right eye (not too tightly, you don't want to distort your left eyeball) while looking at an object through the left eyepiece with your left eye. Turn the center focusing knob (the one located between the two barrels) until you see a sharp image. Next, close your left eye (not too tightly) and look at the same object through the right eyepiece. Rotate the diopter adjustment ring on the right eyepiece until you get a sharp image.
Voila! Both eyes should see the scene in sharp focus. Two separate focus mechanisms are usually needed because each eye focuses a little differently for most people. From this point on, you can now focus for both eyes just by turning the center focus knob to adjust for different distances. You know you've achieved focus when stars appear as pinpoints.
Focus is critical because we'll be looking at not only the Andromeda Galaxy, but also its two galactic companions, one of which looks like an out-of-focus star. I should add that a tripod will help steady the view and therefore bring out more detail, but it's not critical for small- to modest-sized glasses. Just more comfortable!
Choose a dark, moonless night and locate the Andromeda Galaxy in the eastern sky using the method described in last week's installment. In my 8x40s and 10x50s, the galaxy leaps right out, appearing as a diffuse, much-elongated disk of soft, fuzzy light nearly 3° from end to end. With no effort at all, I can easily see the contrast between the much brighter core and the fainter disk. The galaxy's asymmetry surprised me: the southern half looks weaker and narrower compared to the puffier northern half.
Millions of old, evolved stars pack the core, called the bulge, in contrast to the more lightly-populated (and dimmer) disk. This classic dichotomy, seen in many spiral and elliptical galaxies, lies plainly exposed in Andromeda. But the dark dust lanes the define its spiral arcs remain beyond the ken of standard binoculars.
To find Andromeda's brightest companion galaxy, use the trio of 7th-magnitude stars off the galaxy's south end. The farthest north of them points straight to a slight fainter "fuzzy star" — M32. It's an easy pick-up in 8x40s, unlike its brother M110 on the opposite side of the bright nucleus. Also known as NGC 205, this larger, less compact and fainter companion (magnitude 8.9 vs. 8.0 for M32) appears as a featureless haze at first blush. But after several minutes of study using averted vision, I finally eked out its north–south elongation. 7x50s and 10x50s work great to pull this weak piece of mist from the sky background, but nothing definite was visible in the 8x40 glasses.
I have a little surprise for you. Before we sign off, let's drop by another tempting target in the neighborhood, the Triangulum Galaxy located in the petite constellation Triangulum, the Triangle. You'll find it 15° southeast of M31 and well-placed for viewing around 10 o'clock p.m. in late September. Visible as the faintest of smudges with the naked eye under exceptional skies, this patchy spiral galaxy is more than two magnitudes fainter than Andromeda and a tad farther away at 2.7 million light-years.
While difficult without optical aid, an egg-shaped fuzzball greets observers equipped with a pair of 50-mm binoculars under dark skies. A single 8th-magnitude star dots the galaxy's southern rim. With effort, I can discern the slightly brighter central bulge. Unlike Andromeda, M33 has a small nucleus and far fewer stars — 40 million vs. one trillion!
While many of us have access to larger telescopes, it's fun to discover how much there is to see with a much smaller instrument. No matter what we use to examine the night sky — naked eye, binoculars, or big Dob — challenges and fresh points of view present themselves at every level.
Now that you're getting handy with the binoculars, pick up a copy of Binocular Highlights by Sky & Telescope contributing editor Gary Seronik and continue your journey into the night sky!