M3 is a globular cluster visible in the constellation of Canes
It is formed by about 500,000 stars and has a distance of about 33,900 light years from the Earth: its apparent magnitude of 6.2 makes it visible to the naked eye under a dark sky.
With M13 and M5, M3 is one of the three brightest globular clusters in the northern hemisphere. This has meant that it has been studied more than other clusters of its type, and the HR diagram resulting from these studies shows that M3 is a cluster of extremely old stars: it is believed that they are about 10 or more billions of years.
Optic Celestron C9.25 Edge HD f/10
Mount 10Micron GM1000 HPS
Camera Atik 4000 with Starlight Xpress filter wheel 5 positions
Filters Baader 50.8 unmounted
Guiding system Starlight Xpress SXV-AO-LF with OAG, Lodestar
Exposure details L 15x300", bin1 -20C
Total integration 1.2h
Acquisition Maxim, PHD2
Processing Pixinsight 1.8, Photoshop CS5
Location Pian dell'Armà (Italy)
Date 18 February 2017