Side-by-Side Galaxies
Jack Kramer
A favorite sight is two or more galaxies that share the same field of view in our telescopes. They remind us of the Hubble deep field images completely filled with galaxies. They're especially interesting when they appear obviously different. M81/82 and M65/66 are two groups visible each spring and, unlike faint fuzzies, they actually show quite a bit of detail. Both make great targets because they dramatically demonstrate galaxy morphology - the appearance unique to each. These galaxy groups are easy to locate in less than pristine skies, so they're fine for backyard observing and maybe even some of the venues where public star parties are held. And in darker skies there's a bonus - these Messier objects also have nearby NGC companions.
A frequent destination is M81/82 in Ursa Major. The Big Dipper is circumpolar, so these galaxies are visible just about all year long. The following is a star-hopping chart for those of us who don't use a go-to feature on our tele-scopes; it'll help locate this pair starting from the pointer stars of the Big Dipper.
M82 is the most distinctive, being spindle-shaped with a prominent absorption feature diagonally across its center. It radiates strongly at radio frequencies and, together with the disturbed nature seen at visible wavelengths, this sug-gests that M82 experienced a strong outburst at some point in the past. It's classified as an "eruptive peculiar" galaxy. The absorption feature is visible in telescopes of 4-inches aperture. M81 is a more open spiral and appears as a 6.9 magnitude oval glow with a brighter hub. M82 is fainter at magnitude 8.4, but generally appears about the same brightness and size as M81. However, M81 at 24.9'x11.5' is more than twice as large as M82 at 10.5'x5.1'. (The symbol ' here stands for arc minutes.) Because its outer halo is so faint, we're normally seeing only the brighter central condensation of M81. In a dark sky I can easily detect the outer halo in my 12-inch scope, and have just barely seen a bit of spiral structure in a 10-inch. The image here from the Palomar Sky Survey shows both galaxies at integrated visual wavelengths. This gives a better impres-sion of their relative sizes, despite how they usually appear in our telescopes. Roughly due south of M81 is NGC 3077, an almost circular 9.9 magnitude galaxy which lies about as far as is M82 in the opposite direction.
The other group of galaxies, M65/66, is an easy star hop beginning at Theta (?) Leonis, the star located at the right angle of the triangle that is the "rear haunches" of Leo the lion. Head due south to the first bright star (73 Leonis), then a short distance east to the next bright star, and you'll be about in the center of a field containing M65 and M66, plus NGC 3628, an additional spindle-shaped galaxy.
M65 and M66 are about the same length along the major axis, but M66 is almost twice as wide. Both galaxies are around 9th magnitude. For comparison purposes, the scale of the Palomar Sky Survey image is the same as that of M81 and M82. My notes indicate that in a 10-inch scope M65 exhibited an elongated central hub, but no further sur-face detail. M66 showed knots of brightness scattered throughout the envelope, plus a spiral arm. Both galaxies take magnification well. NGC 3628 is easy to see at mag-nitude 9.5 and is almost edge-on. It had a mottled surface in my 10-inch, with an absorption feature clearly seen split-ting the galaxy along the major axis. Using a wide field eyepiece, all three galaxies fit in the same field of view in my 4-inch refractor. How could Messier miss NGC 3628 when he cataloged its two neighbors? Note that these ob-servations were all from dark sites - light pollution dimin-ishes the ability to spot any detail in these galaxies.
On the star hop down to M65/66, you'll pass another gal-axy, NGC 3596. It appears perfectly circular, with a di-ameter of about 4.1'. At magnitude 11.3, it should be visi-ble in many of our telescopes; however, it has a low sur-face brightness, so requires a reasonably dark sky. From a dark site I saw it easily in a 10-inch scope, where the brighter hub stood out against the circular envelope. This is one of the pleasures enjoyed by the star hopper - the ser-endipitous "discovery" of other objects along the star hop-ping route.
