M76: the Dumbbell Nebula’s neglected little brother
2013 November 27
While Messier 27, the Dumbbell Nebula, is probably one of the favourite Messier objects to observe and image, its little brother M76 – the Little Dumbbell – seems to be rather overlooked. Certainly it is not as spectacular as M27 – but is definitely a challenge, being probably the faintest object in the Messier catalogue. M27 is of course somewhat larger (on the sky), about 8 arcminutes long, whereas M76 is about 3 arcminutes. But M27 is closer to us. Distances to planetary nebulae are not particularly accurate, but estimates put M76 about three times as far away from us as M27, at around 3,500 light years; so probably the two objects are really about the same size.
There are two distinct lobes to this planetary, and for many years it was thought to be two nebulae. William Herschel observed it so, and hence there are two NGC numbers for the two lobes – 650 and 651. Although located in Perseus, I find star hopping to it easier by starting in Andromeda. I usually start at 51 And, which is located at the end of the northern part of the ‘V’ of stars originating at Alpheratz, though if you find locating 51 And tricky, you can start at Almaak (g And) and head northwest to find 51. From 51 And it is a short jump northeast to 4th magnitude f And. Track north nearly a degree to a distinct yellow 6th magnitude star, then M76 is a short 11 arcminutes westwards.
Observing M76 is difficult with a small scope; probably at least 150mm aperture will be needed though it is a lot easier with 200mm aperture or more. Use higher magnification of ´100 to ´200 once you have found it. And it would be interesting to note the effect of filters on this object. OIII should give a better view, but UHC may disappoint.
For imagers the challenge is the small size of the nebula – requiring longer focal length to give more image scale. And of course longer focal lengths mean longer exposure duration and greater vulnerability to guiding and periodic errors. The central star is a faint mag 16.6 hot blue star, which will be beyond most visual observers, but should not be too difficult for imagers.
Other ‘dumbbell-esque’ planetary nebulae worth hunting down in the coming months include NGC 40 in Cepheus and NGC 2346 in Monoceros. Perhaps you have your own favourites – please let me know and send in your own observations.
Callum Potter, Director, Deep Sky Section
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