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The other Andromeda

Seek out treasures beyond the galaxy.
Harrington

The mere mention to an amateur astronomer of the constellation Andromeda will probably conjure up images of M31, the Andromeda Galaxy. While that is a wonder to behold through telescopes and binoculars alike (see my December 2016 column to find out more), this month, I want to examine the other Andromeda — that is, worthwhile targets that are often bypassed because M31 is so captivating. There is more to meet the eye within the bounds of our celestial princess, if you know where to look.

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Andromeda holds two bright stars in Alpheratz (a) and Mirach (b), which offer a stunning color contrast.
Tony Hallas
Let’s begin with the constellation’s two brightest stars, Alpheratz (Alpha [α] Andromedae) and Mirach (Beta [β] Andromedae). The two are separated by 14°, or about two binocular fields. Compare one against the other; they are great examples of color contrast. Alpheratz, a hot type B subgiant star, has a blistering surface temperature of 13,000 kelvins (23,000 degrees Fahrenheit or 12,700 degrees Celsius). That’s about twice our Sun’s. It lies 97 light-years away from our solar system. Mirach is a larger, cooler class M red giant twice as far away as Alpheratz. Its surface temperature is believed to be only 3,800 K (6,400 F or 3,500 C), or about half the Sun’s. Their color difference should be immediately apparent with binoculars, but if not, slightly defocusing the images will intensify the effect.

Our next Andromedan targets are most easily found by referencing the neighboring constellation to the east, Triangulum. From Mirach, scan 12°, or again about two fields, due east to Beta and Delta (δ) Trianguli. From there, extend a line to the northwest from Delta through Beta, and back across the border into Andromeda. About a binocular field beyond Beta, you’ll spot a colorful binocular double star. The brighter of the pair is 56 Andromedae, a yellow giant star. Its neighbor, cataloged as SAO 55102, is just 3.5' to the northwest. Despite appearances, they are actually nowhere near each other in space. While 56 And is 316 light-years from us, SAO 55102 is another 605 light-years farther still.

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Planetary nebula NGC 7662, sometimes called the Blue Snowball, offers observers the blue-green remains of a Sun-like star that has ceased to exist.
Derek Santiago
You’ll also notice a third 6th-magnitude star, SAO 55082, 14' to the pair’s southwest. All three create a slender triangle of 6th-magnitude stars that easily fits into the same binocular field.

When he gazed toward that triangle through his binoculars, the late deep-sky devotee John Davis imagined a golf putter. He saw the triangle as the putter’s blade. Its handle is formed from five additional stars extending for 1.5° northwest from the triangle’s tip. The handle ends at 6th-magnitude SAO 66630, another orange star.

Now, look for a soft glow less than a degree northeast of 56 Andromedae. See it? It will look like a round, grayish smudge of light about as large as the Full Moon. That’s open cluster NGC 752. With an overall magnitude of 5.7, it is faintly visible to the eye alone with clear, dark skies. The cluster is home to about 60 stars, none of which is brighter than 9th magnitude. A few faint specks just might peek out with 50mm binoculars, while about a dozen show themselves through 70mm and larger apertures. The remaining stars seem just beyond the limit of visibility, blending together to make the cluster appear “granular.”

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The bright open cluster NGC 752 is a delight for binocular owners.
Anthony Ayiomamitis
Our last stop this month is more challenging than the rest. Planetary nebula NGC 7662, nicknamed the Blue Snowball, lies in the northwestern section of the constellation. Beginning at Alpheratz, scan about 16° to the north-northwest until you come to three 4th-magnitude stars — Iota (ι), Kappa (κ), and Lambda (λ) Andromedae — set in a distinctive north-south arc. From Iota, the arc’s southernmost star, slide 2° west to 6th-magnitude 13 Andromedae. NGC 7662 is just half a degree farther southwest. Although it looks faint, its color should give it away. Look for a pale blue 8th-magnitude “star.” Of course, there are many lookalikes in the same area. If you can’t determine which is the planetary by its color, try alternating between direct vision and averted vision as you examine each point. The planetary will appear to blink, while stars will not. At 12x and higher magnifications, NGC 7662 will begin to reveal its nature by displaying a tiny, elliptical disk.

Do you have a favorite binocular object? I’d love to hear about it and share your observations in a future column. Drop me a line through my website, philharrington.net. Until next month, remember that two eyes are better than one.

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