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Deepsky Top-100 (17): M 36, the Butterlfy Cluster
Towards the end of the year, Auriga climbs higher and higher in the night sky, and within its borders lie three of my favourite open clusters, M 36, M 37 and M 38. All three open clusters will be included in my Deepsky Top 100, but I will start with M 36, which I observed and sketched this week (8 November 2005).

Le Gentil discovered M 36 in 1749, while he was working as an assistant of Jaques Cassini at the Paris Observatory. Messier observed M 36 on 2 September 1764. It lies in Auriga, near the galactic anticenter, at a distance of 4100 light years. When you look in this direction (Auriga), you look away from the galactic centre, towards the nearest stretch of our galaxy's rim.

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Click to enlarge (image from SkyTools 2 by CapellaSoft)


M 36 has a diameter of 12' and a visual brightness of magnitude 6. Its brightest star is a magnitude 8.86 B2 main sequence star. M 36 can be found roughly halfway between M 37 and M 38, about 8 degrees tot the east of Iota Aurigae. When the seeing in my backyard is "moderate" (mag. 4.7 visual) I can see M 36, M 37 and M 38 in my 8x50 finder scope as three faint patches of light.

As it is with many star clusters, most people "see" some kind of pattern in these objects. Some observers report that M 36 looks like a crab, others see a crooked Y, X or a big cross. I want to add one to the list. To me, at first glance, M 36 looks like a butterfly when looking through my 8-inch f/10 Klevtzov using a Televue 32mm plossl (field of view about 48' magnification 62x). Using a 20mm eyepiece, magnification 100x, I counted about 40 stars, ranging from magnitude 8 to 12.5. There are several arcs and small groups (2 or 3) of stars visible. I did not detect any form of nebulosity or background haze from unresolved stars. But when I increased the magnification, more (fainter) stars became visible. The sketch below should give you an idea. Anyway, let me know what you "see" when you go out and observe this beautiful open cluster.


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This sketch was made on 8 November 2005, from 22.30 UT till 23.15 UT. The instrument used was the TAL 200K, a Vixen Lanthanum 20mm, magnification 100x and field of view approx. 30'. North is up and west is to the left.
Posted by Math on 11/13 at 10:17 AM
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