How would you like to see what's behind the stars? When I was a boy I couldn't wait to find the Orion Nebula, the Hercules globular cluster and many others with my telescope and binoculars. But first I had to learn the bright stars and a few constellations to help me find the way to the deep sky.
Deep-sky objects are non-stellar celestial objects that usually require optical aid to see. They include all those magnificent galaxies, star clusters and nebulae (clouds of dust illuminated by stars) famously pictured with the Hubble Space Telescope. The brighter naked-eye stars are typically dozens to hundreds of light-years away, while deep-sky objects are often much more remote, from thousands to billions of light-years distant. Deep.
Once I became familiar with the brighter stars I used them to star-hop to a nebula or cluster. I'd lay open my star atlas and note the position of a deep-sky target with respect to a star I could easily identify. I'd mentally draw a path to the object, then point my binoculars at it and slide a little this way and a little that way until I spotted what I was looking for. Often, I had to use more than one star to get there the same way you'd carefully chose steppingstones to cross to the other side of a river.
You can hunt the deep-sky, too. How would you like to see three star clusters and the closest, biggest galaxy beyond the Milky Way? All are within a stone's throw of the familiar W of Cassiopeia and visible in a pair of 35mm or larger binoculars. You'll need a clear, preferably moonless sky for the hunt and warm clothing. Clothing is important for comfort's sake. Properly dressed, you can observe in a relaxed state of mind, which increases the enjoyment of stargazing.
Our deep-sky targets are the Andromeda Galaxy, the Perseus Double Cluster and NGC 752, a bright but neglected star cluster in Andromeda. Depending on the size of your binoculars and sky darkness they may all strike you as little more than hazy patches of light at first glance. Most things do in typical amateur instruments. Only larger telescopes and time-exposure photographs show the kind of detail we've grown accustomed to seeing in published images.
Deep-sky objects appear more delicate and nuanced and require an observer to spend at least a few minutes to appreciate what's there. The act of focusing your attention will not only reveal more detail than you thought was present at first encounter, but there are spillover benefits. Visual concentration sharpens our powers of observation of other natural phenomena.
We're going to use Cassiopeia as our steppingstone to the deep-sky. Start around 8 o'clock local time in mid-February and allow about 10 minutes for your eyes to adapt to the darkness. Look halfway up in the northwestern sky to spot the W of Cassiopeia. This time of year it's tilted on its side and better resembles the Greek letter sigma, written as Σ.
While looking up, raise the binoculars to your eyes and focus sharply on the top two stars of the W. Then slide about one binocular field of view (~6°) up and to the left. You should now see two dense clumps of stars, one on top of the other. This is the Perseus Double Cluster, comprised of two paired star clusters, NGC 869 and 884, that lie 7,500 light-years from Earth. Each is 4th magnitude, bright enough to see with the naked eye from a dark sky.
In my 8x40s I see two dense piles of starry gems, each with its own distinctive appearance. It was just an impression, but the stars in both appeared to spill over the sides as if heaped too high. Both are young clusters, born from gas and dust clouds (nebulae) 12.8 million years ago. The Pleiades in contrast are much older, roughly 100 million years.
After you've taken your measure of the Double Cluster, point your binoculars at the bottom three stars in the W that form a bright equilateral triangle. Then slide about three binocular fields to the left until you see something fuzzy. That's the Andromeda Galaxy, located 2.5 million light-years away. It's the nearest large galaxy to our own and contains about a trillion suns in a flattened disk 220 million light-years across — twice the size of the Milky Way!
Andromeda is so far away that its faint stellar multitudes blur into a cigar-shaped puff of light 2-3° long. One detail stands out — the galaxy's brighter core, where the stars are more densely concentrated. Can you see it? Like the Double Cluster, the galaxy is faintly visible without optical aid under dark skies.
From the Andromeda Galaxy, follow the short arc of stars to its left to the bright star Mirach. Then slide about two binocular fields straight up to find the sprawling 6th magnitude star cluster NGC 752. It looks like a smoky patch about 1° across shot through with faint stars. While nowhere near as compact as the Double Cluster, it's still a true star cluster. All of its members hang together by their mutual gravities as they travel across space like a school of fish in the ocean. NGC 752 is ancient — about two billion years old — and 1,300 light years away.
I've shown you one way to star-hop to each of our featured deep-sky objects, but like driving to a destination, there's often more than one way to get there. With the help of the map you can choose to start at a different star and arrive at an object by an alternate route. More power to you! Finding your way in the sky takes advantage of your own ingenuity. The more you use it, the more satisfying your journey.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.