This month’s imaging object is M15 [NGC7078] the Great Pegasus Cluster, a very nice Globular Cluser in the constellation Pegasus. This is a large globular with a diameter of 18 arc minutes (M13 is 21 arc minutes) and lies at a distance of 31,000 light years. As it is a fairly small object you do better with longer focal lengths for this one and as is usual for globulars keep the sub-exposure time down a bit so that you can resolve the core stars. M15 contains some hidden secrets! One of these is Pease 1, a 14th magnitude planetary nebula on its north-eastern side. M15 also contains a large number of variable stars – nearly 100 have been logged so far. It was discovered in 1974 that M15 was a source of X-rays, these are believed to emanate from supernova remnants. So, for a decent image of M15 you want a reasonable focal length for an appropriate image scale, shortish subs of maybe 3-minutes duration depending on your f#, and finally, as usual, as many subs as you can get for a nice smooth finish 🙂
We are well and truly into winter imaging evenings now with long dark nights – let’s just hope we get a few clear Moonless ones as well.
Until November’s IOM – clear skies and happy imaging.
