Sky Object of the Month – April 2018

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Sky Object of the Month – April 2018
(Courtesy LVAS Observer’s Challenge*)

Messier 81 and 82 – Galaxy Pair in Ursa Major
Messier 81 (“Bode’s Galaxy; Magnitude 6.9; Size 27’ X 14’)
Messier 82 (“Cigar Galaxy”; Magnitude 8.4; Size 11’ X 4’)

When preparing a list of sky objects to show with my telescope at public star parties, I tend to avoid galaxies. To the uninitiated observer, a galaxy has the appearance of a hazy blob – for all the world, nothing more than fog remaining when someone breathed on the eyepiece. Even the great Andromeda Galaxy (Messier 31) fails to awe the first-time viewer. I make an exception where the galaxies M81 and M82 are concerned. Sure, they’re still “faint fuzzies,” but the two are just 38 arc-minutes apart and appear together in the same low-power field. The sight of an oval-shaped patch (M81) next to a spindle-shaped one (M82) is intriguing at the very least.
M81 and M82 lie about 12 million light years distant. M81 is a spiral galaxy whose 90,000 light year diameter makes it slightly smaller than our Milky Way. Small aperture telescopes reveal the nucleus, while a 6-inch instrument will begin to show hints of the spiral arms. M82 is smaller, with a diameter of some 37,000 light years. For many years, M82 was thought to be an irregular galaxy. Recent studies hint at a spiral structure, the irregular appearance a result of an accelerated amount of star formation perhaps due to the gravitational influence of M82.
To locate M81 and M82, center your finderscope on an area marked by a line drawn from Phecda (gamma [γ] Ursae Majoris) through Dubhe (alpha [α] Ursae Majoris) and extended an equal distance beyond. A careful sweep with the finderscope or the main scope with a low-power eyepiece in place should reveal the two.

In the spring of 1993, a supernova was discovered in M81, reaching a peak magnitude of 10.5. In January, 2014, M82 got its turn, producing a supernova (2014J) that also reached magnitude 10.5.
If you live in a truly dark sky area (we’re talking about a place with a limiting magnitude in the order of 7.0!), try to see if you can pick out M81 with the unaided eye. A handful of amateur astronomers have accomplished this eagle-eyed feat, most notably Astronomy columnist Stephen James O’Meara.

M81 and M82 were discovered by the German astronomer Johann Elert Bode on December 31, 1774, then independently by the French comet-hunter Pierre Méchain 5 years later. Méchain reported the pair to his contemporary Charles Messier, who observed and cataloged them in early 1781.

Glenn Chaple for the LVAS

M81 (left) and M82 (right) Mario Motta M.D.

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