At a distance of about 11 million light years, the Messier 81 (M81) galaxy group lies nearly overhead in the late northern spring and early summer and presents a handful of intriguing targets for backyard stargazers. This aggregation of gravitationally bound galaxies lies mostly in Ursa Major with some spillover into Camelopardalis. It’s one of the nearest galaxy groups to our own, and it contains some 40 galaxies and a total of about a trillion stars.
The brightest members of this galaxy group are the dazzling 7th-magnitude spiral M81 and its jumbled 8th-magnitude peculiar companion M82. The two lie just north of a line from gamma Ursae Majoris (Phecda) across the bowl of the Dipper and through Dubhe about a distance equal to the separation of these two stars. They fit nicely in a one-degree field of view, and even a small pair of binoculars show the pair in dark sky. Observers with better eyes than mine can see M81 without optical aid under ideal observing conditions.
In a telescope at 80x-100x, M81 appears clearly oval in shape with a bright nucleus surrounded by fainter oval haze. A pair of 11th-magnitude stars lie at the southern end of the halo. Use averted vision and much patience in dark sky to glimpse the ethereal spiral arms. More aperture will help. The spiral is a favorite of deep-sky imagers because of its brightness and majestic spiral arms.
M82, by contrast, presents a far more interesting view for a small telescope. It’s a ragged cigar-shaped edge-on spiral in the throes of an intense round of star formation caused by gravitational nudging from M81. Even at low power, the galaxy is clearly needle-shaped with a striking mottling visible throughout. At 80-100x, you can see the central dark region that appears to split the galaxy in two, and on nights of good seeing even finer degrees of detail become visible. In infrared light, M82 is the brightest galaxy in the sky, likely because of intense star formation in its spiral arms.
Though none are as bright as M81 or M82, the M81 Group includes a few more bright members within reach of a small telescope, either visually or with a small camera for electronically-assisted astronomy (EAA):
- NGC 2403. One of the closer members of the group, just 8 million light years away. This little galaxy is rich with clots of emission nebulae where new stars are formed. It’s similar to the Triangulum Galaxy (M33) but nearly four times as distant. A binocular target in dark sky, this 9th-magnitude galaxy shows an appreciable amount of detail in a 10” Dob.
- NGC 2366 in Camelopardalis, a small 11th-magnitude irregular galaxy similar to the Magellanic Clouds and a possible nearby example of a ‘green pea’ galaxy
- NGC 3077, a small, round, and slightly mangled 10th-magnitude elliptical not far in the sky from M81 and within the same one-degree field of view of M81 and M82. Its disrupted appearance arises from gravitational interaction with M81.
- NGC 4236, a modest 10th-magnitude barred spiral that’s remarkably large, about 20’x7’, but rather dim
- And if you’re up for a challenge, try for IC2574, a dim 13th-magnitude dwarf spiral. Currently in a state of rapid star formation, this hard-to-see galaxy holds about 90% of its mass as dark matter!
The M81 group includes a few dozen far dimmer members, all much more challenging in backyard scopes. Like our Local Group, the M81 group and most nearby galaxy groups are outlying members of the Virgo Supercluster, an immense congregation of galaxy towards which M81 and the Local Group are slowly moving, a phenomenon known as Virgocentric Flow.
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