I setup my ZWO ASI2600 OSC on 5 inch refractor. M5 is so large that imaging with the 11 inch SCT would have resulted in the globular taking up almost all of the field of view. Used ZWO ASI290 on 90mm refractor for autoguiding. I again had difficulty with ASTAP platesolve, but this time with angle rotation. I then realized that the autoguider was drifting way too much. I did not recalibrate after switching to the 90mm. So I recalibrated the PHD2 and things went much smoother.
I was able to take 175 images of 1 minute with temp -10C and gain 100 binning 1x1. With this many sub frames, I was bit fussy about selecting the best frames dwindling down to the best 149 images. That is one good thing about globular clusters... since it is stars, you don't have to acquire several hours of images to get decent result. I used Pixinsight to process and found that it easily aligned sets of sub-frames that were almost 90 degrees off (due to rotator and platesolve 'issue'). Only modest image processing performed. I found that in cases like globular clusters, it does not help to perform any type of star reduction, since it impacts the cluster.
M5 is a globular cluster in Serpens. It is about 24,500 light years from Earth and has apparent magnitude of 5.6. This makes it just barely observable with naked eye, but you would need very good conditions to do so. This object is so bright it was first discovered by Gottfried Kirch in 1702! Like Charles Messier, he found M5 while observing a comet. Messier 'found' it in 1764. M5 is also one of the oldest globular clusters in the Milky Way.
Roger
- M5 Master_DBEdiv_EzDN_PCC_ArcSinH_Curves.jpg (13.91 MiB) Viewed 700 times
