So many galaxies, so little time! A good place to begin an evening of galaxy hopping on a northern spring or summer night is with the Messier galaxies M81 and M82 in the constellation Ursa Major (see above). Conveniently located by drawing a line through the Big Dipper stars Phecda and Dubhe and extending it an equal distance beyond the Big Dipper asterism, this is probably the finest galaxy pair in the sky. Separated by just 38 arc-minutes, both fit into the low power field of a small telescope. With a 22mm Panoptic eyepiece in my 8″ EdgeHD telescope, I had 93x and a field of view of 45 arc minutes, so I had to slew the mount a little from one to the other to see them both well.
At magnitude 6.8, M81 is one of the brightest galaxies in the sky, bright enough to be glimpsed with the naked eye by the most owl-eyed observers, a category which does not include me. In the telescope it is a big, bright oval, fading smoothly from center until vanishing with an uncertain boundary into the surrounding blackness. Although my current site in the Mojave Desert is quite dark, I could not see the full extent of M81. Its delicate spiral arms, which photograph so beautifully, are faint and hard to see. I recall seeing them only once, using my 10-inch reflector from the Winter Star Party in the Florida Keys. Maybe your eyes are keener than mine. Two embedded foreground stars, of magnitude 11 and 12, are easily seen toward the south side of the galaxy. In 1993 a third star appeared near them, and it was a legitimate member of the galaxy, though one that was meeting its end as a supernova. A pair of brighter foreground stars lie off the galaxy’s southwestern side. One of them is actually a neat little double star, SAO 15018, two similar stars of about magnitude 10.5, separated by 9 arc-seconds, easy in almost any telescope.
M81 has a little phantom companion, UGC 5336, lying just off its eastern flank. Faint at magnitude 14 and diffuse, I had only the vaguest sense of ever seeing this elusive glimmer. I did see a faint star of magnitude 13.7 that lies just on its southern edge. If you can’t readily see this star, the galaxy is probably beyond you. The galaxy does show up as a collection of faint blue clumps in my image of M81.
A little jog to the north brings us to M82. Though smaller and fainter than M81, M82 is one of the most detailed galaxies in the sky for small telescopes. Its surface brightness is high, meaning it takes high magnifications well. We see it nearly edge on, resulting in a fat, fairly symmetrical cigar shape. Gravitational interactions between the massive M81 and its close neighbors have caused a lot of trading of gas and dust. Some of this material has poured into M82, resulting in great bursts of star formation. Signs of these processes can be seen in the eyepieces of our humble telescopes. M82 is riddled with dark lanes and intrusions that give the middle part of the galaxy a lumpy appearance. Some of the bright areas that show through the gaps in this dark network and so small and intense they almost look like stars.
My image shows signs of the gravitational warping of M82’s disk, and also shows traces of red, spidery filaments emanating from the core. This is apparently material blown out of the galaxy by a spate of supernova explosions, glowing mainly in red hydrogen alpha light, and would be difficult to see visually in any telescope.
A third member of the M81 galaxy group is far less spectacular but still easy to see. NGC 3077 is a small galaxy that is undergoing some starburst activity of its own. In my eyepiece at 93x is appears slightly elliptical and concentrated toward the center. I had the impression its brightest part was offset in the direction of M81.
Delving into the adjacent constellation of Canes Venatici, the Hunting Dogs, we come upon the impressive edge-on galaxy NGC 4631, sometimes called the Whale Galaxy, which is located roughly between the second magnitude star Cor Caroli and Gamma Comae Berenices. Spanning 14 arc-minutes, this large object looks half as long as the Moon is wide. It’s a lovely sight in my eyepiece at 93x, looking like a photograph seen in a dimly lighted room, or like a shimmering, elongated, silver candle flame, obviously wider on its eastern end. If it’s a whale, it also has a calf, or maybe just a remora, in the form of NGC 4627, a small elliptical galaxy lying just off the Whale’s northern flank. At 12th magnitude it’s four magnitudes fainter than its companion, faintly visible, but not impressive.
A far superior nearby sight is the “Hockey Stick Galaxy”, NGC 4656, which lies half a degree southeast of the Whale. Smaller and fainter than the Whale, it’s still easily visible and offers some detail. Also edge-on, it starts out fairly brightly and then narrows and tapers out toward the northeast, looking like a line of faint, clumpy blobs. The “blade” of the hockey stick which gives it its name veers off toward the east. Its presence was only suggested in my eyepiece, though it photographs clearly. It has its own NGC number, 4657.
As you study this galaxy you realize there’s more to it than is obvious at first glance. It actually continues toward the southwest from that brightest region, doubling its apparent length, though that southwestern half is much fainter than the other.
Skipping back north to Cor Caroli, we find also its fainter neighbor, Chara, or Beta Canum Venaticorum. These two form a convenient marker for our next target, M94, which lies between them but almost two degrees toward the north. This galaxy is prominent in almost any telescope, even under considerable light pollution, because its central core is very concentrated and intense. Seen under a dark sky, that bright core is surrounded by a round, fainter halo. Averted vision showed a hint of mottling that suggests the tightly wound spiral arms of this galaxy.
Intriguing as all this is, my image reveals details beyond the reach of any backyard telescope, including a bright inner ring of rampant star formation, and even more remarkably, a large, dim, diffuse outer ring of stars that suggests this galaxy’s turbulent history, a feature I didn’t even know existed until I did some later research.
Still within the borders of Canes Venatici, tucked beneath the Big Dipper’s star Alkaid, we come to the next major “skymark” of tonight’s agenda, the famous Whirlpool Galaxy, or M51. If you’ve failed to see spiral arms in M81 or M94, you have a good chance of success with M51. My 8” scope at 93x shows the bright, compact core of the Whirlpool itself and the nearby, similarly bright interacting galaxy NGC 5195. Clearly visible around the core of the Whirlpool is its large disk, presented to us face-on, and the winding dark lanes that define its spiral arms are apparent. It’s a beautiful sight from a dark sky location, and it only gets better with every increase in aperture. In a 12” scope the arms are so plain and distinct you get the sense of viewing a black and white photo with the lights turned low. The distorted bridge of stars that connects the two galaxies is fainter and harder to see, but if you’re looking for spiral arms, you’ve come to the right place.
My 92mm refractor presents a subtler but still arresting view. The bright cores of the two galaxies are still obvious, and 5195 show an almost stellar brightening. The disk of M51 is nicely visible at 75x, but I no longer have a sense of the spiral arms at this aperture.
M51 has its share of minor galactic neighbors. The most prominent is NGC 5198, an easy little blur lying about 2/3 of degree due south of M51. It’s involved with a few faint stars of magnitude 14 or so. It’s actually several times farther away than the Whirlpool.
Finally, try for NGC 5173, a minute fleck of light lying about a degree SW of M51. Faint and tiny at magnitude 12.5, it shows no real detail in an 8”, but it’s there for you to look at. It’s flanked by even fainter galaxies on either side, which I didn’t see. I suspect both are beyond the reach of an 8” telescope.
If you find yourself looking at NGC 5173 one fine night, you can be fairly sure you are the only person in the world viewing that particular object at that moment. In fact, you will be among a pretty small number of people who have ever seen it.
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