We explore deep-sky riches within a stone’s throw of Capella, one of the season’s brightest stars.
Goats and amateur astronomers have at least one thing in common: We like to forage. Goats are discriminating and seek the tastiest edibles they can find. You and I will go to the ends of the sky on the coldest or most mosquito-ridden nights to hunt up a nebula or comet we've never seen before. Our kindred spirit is Capella, the Goat Star, the brightest luminary in the constellation Auriga, the Charioteer.
The name Capella derives from the Latin word "capra" meaning goat, and its association with goats goes back to the days of Mesopotamia. Modern observers might be surprised that such a prominent star would be named for a common farm animal. But goats were one of the first animals to be domesticated — as early as around 8000 BC — and an important source of meat and milk for neolithic farmers.
Capella will be our touchpoint for a foray into the deep-sky hinterlands. At twilight's end the star is already halfway up the northeastern sky and crosses the meridian near the zenith from mid-northern latitudes around 10:30 p.m. in early January. Your best viewing time is early evening before it climbs so high that (depending on your scope) you'll need to stand on tippy toes to reach the eyepiece. What appears as a single star is really a pair of yellow giants in close orbit 42.8 light-years from the Sun. If you include a second pair of distant but gravitationally bound red dwarfs, Capella multiplies into a small flock of suns.
We won't stray far. Within a circle of radius about 3° centered on the Goat Star there are more than a dozen star clusters and attractive double stars for instruments 3-inches on up. You can spend a full evening here and hardly move the telescope — one of my favorite ways to observe. All my observations were made with a 15-inch reflector from a suburban-rural location under moonless skies.
Located just ½° south of Capella and nearly overwhelmed by its light you'll find the delicate open cluster Patchick 3. Amateur astronomer Dana Patchick of California discovered the object — a true cluster — on February 5, 2003, while searching for objects potentially hidden in the glow of bright stars. He was using an old Coulter 13.1-inch reflector at the time and writes:
"The key to enjoying this cluster properly is to have the proper balance of magnification, sky darkness, and I would also say — to position Capella on the edge of the field. It will then appear as a tantalizing and delicate sight to the eye. It is a weak one (cluster) and has be 'teased out' very gently."
With Capella safely hidden off-field and a magnification of 64× I see a moderately compact group of about 25–30 stars of magnitude 11–12 and fainter, presenting a slightly hazy appearance. At 142× the haziness disappears and a C-shaped arc of stars extends across the group. Elongated east-west, Patchick estimates the cluster's size at around 4' × 2.5'. Once you've studied it, slide Capella back into the field and try to keep both the cluster and star in view at the same time for an eye-opening experience.
Although observers continue to invent new telescopic asterisms — distinctive but unrelated stellar arrangements — Pat 3 may be one of the last true open clusters to be discovered visually by an amateur. An 8-inch or larger telescope under dark skies should have no problem clawing this dainty from Capella.
One degree southwest of Pat 3 you'll run into the large, loose, and bright cluster ASCC 13, discovered in the early 2000s during a search of the All-Sky Compiled Catalog of 2.5 Million Stars (ASCC-2.5). A triangle of 8th-magnitude stars anchors the this super-easy-to-see object, but with a diameter of 1.4° it overflows the field of view even at my lowest magnification. Use a wide-field scope or binoculars to better appreciate the glitter here.
About a degree north-northwest of ASCC 13's center (or 1° south-southwest of Capella) look for another sparse but much smaller cluster called Froebrich-Scholz-Raftery 716, or FSR 716. Glimmering from around 14,700 light-years away there's not a lot to see here. I counted half a dozen faint stars from magnitude 13.5 to 14.8 in an arc about 5′ long at 245×. Despite its faintness the group is compact and visible even at 64× as a dab of granular haze.
Now return to Capella and slide 1.1° southeast and you'll likely see absolutely nothing . . . at first glance. But if you have at least a 12-inch scope and muster the magic of averted vision you might detect an innuendo of light some 12′ across that is the open cluster Berkeley 18.
Using 64× and 142× I finally did confirm a ghostly presence unblemished by a single cluster member. That's funny because 300 stars reside here. Of course, I should have checked in advance — the brightest shine at only magnitude 16! I reobserved the object from a much darker sky at 142× and succeeded in getting fleeting views of many faint pinpoints at the limit of vision. A 24-inch telescope would have a field day with Berkeley 18, the reason it's now on my list of things-to-look-for-through-monster-Dobs at the next star party. Remember those?
Let's take a break from our cluster-hop to enjoy the striking little pair Σ669 located between Be 18 and Pat 3. It fits into that special class of low-power close double stars that provide the thrill of seeing two stars snuggled tightly without needing to increase the magnification and spoil the crispness of the image. Primary and secondary shine at magnitudes 8.4 and 9.0, respectively, with a separation of 9.8″ in PA 278° (west). At 64× the pair resembles Jupiter and Saturn during their recent Great Conjunction.
For a special treat, use medium magnification and look about 2' east-northeast of the double for a fainter pair of stars (magnitudes 12 and 13) with approximately the same separation and position angle. To my eye this mimic-duo struck me as uncanny, as if it were a secondary reflection of Σ669.
Slightly more than a degree northeast of Be 18 look closely for the open cluster NGC 1883, a faint but well-condensed grainy haze 5′ across with a 9.9-magnitude star pinned to its northeast side. Star Clusters by Archinal and Hynes caps membership at just 30 suns, but I saw closer to 40. While NGC 1883's overall magnitude is 12, its brightest members check in at 14. Medium magnifications of 100–150× will resolve several dozen stars against a hazy backdrop of fainter members. Take a look and tell us what you see.
If you now head back west toward Capella you can't miss the pretty double star Σ681. Bright and easy to split in any scope, 23.2" separate the 6.6-magnitude primary from its 9.2-magnitude companion in PA 183° (south). From here it's a 1.7° star-hop northwest to NGC 1798, a rich open cluster similar in size to its neighbor, NGC 1883, but brighter at magnitude 10 with around 50 members. Its round shape and shimmery richness at 64× reminds me of a sparse globular cluster. Both NGC 1883 and NGC 1798 are remote objects, at distances of 15,700 light-years and 11,600 light-years, respectively, which accounts for their misty appearance.
From here you can either star-hop back to Capella and continue tracking west or repoint your scope at nearby Epsilon (ε) Aurigae, the apex of the triangle-shaped asterism dubbed "The Kids" some 2° to 3° southeast of Capella. The open cluster Berkeley 15 lies ½° north of Epsilon and 5′ northeast of a 7.3-magnitude star. At 64× I see a handful of 13th-magnitude stars scattered atop a hazy glow of fainter members (35 in total) about 5–6′ across. Increasing the magnification reveals additional fainter stars.
The Berkeley Open Cluster Catalog is a compilation of 104 objects, many discovered on Palomar Observatory Sky Survey plates by astronomers at the University of California (Berkeley) in the late 1950s. The clusters are mostly faint and old, but many are accessible to amateur telescopes. Berkeley 14, located 35′ southwest of Epsilon and 7′ northeast of a 7.4-magnitude star, definitely falls into the faint category. With the brightest of its 30 members at magnitude 16 (my scope's threshold) the best I could do was suspect a small, glowing presence at the location using averted vision and 142×.
Our final stop is the dubious yet convincing cluster lookalike dubbed Skiff 2 found ½° southwest of Berk 14. Likely a chance gathering of unrelated stars, it puts on a good act. I see a roughly triangular-shaped patch 4′ across with a dozen suns between 10th and 13th magnitude at low magnification.
I hope you have the opportunity in the coming nights to graze on our featured deep-sky "hillside." One thing leads to another in this rich region of the winter sky, so don't be surprised if you roam and find your way to other wonders.