About image NGC 7217 is a spiral galaxy in Pegasus constellation, about 50 million light years away. Its main feature is the presence of several concentric rings of stars in its nucleus: three are the main ones, the outermost of which is the most rich in gas and the one that hosts the largest number of episodes of star formation, to which add more, more interiors to the first three, discovered by the Hubble Space Telescope. Another noteworthy feature is the presence of a certain number of stars rotating around the nucleus of the galaxy in the opposite direction with respect to most of the others, and of two distinct star populations: one of intermediate age in the innermost regions, a younger one but poorer than metals to the outside. These characteristics are believed to have been caused by fusion with another galaxy and indeed some computer simulations show that NGC 7217 could be a large lenticular galaxy, which merged with one or two smaller gas-rich, becoming the galaxy to spiral we see today.
Technical data Optic Celestron C9.25 Edge HD f/10 Mount Losmandy G11 with Ovision worm and FS2 Camera Atik 4000 with Starlight Xpress filter wheel 5 positions Filters Baader 50.8 unmounted Guiding system OAG LB Astro Proxima with Lodestar Exposure details L 24x600" bin1 -20C R 7x420" bin2 -20C G 7x420" bin2 -20C B 7x420" bin2 -20C Total integration 6.5h Acquisition Maxim, PHD2 Processing Maxim, Photoshop CS5 SQM-L 21.04 Location Pian dell'Armà (Italy) Date 11 August 2015, 12 August 2015