The Palomar Clusters were discovered by some of the most famous astronomers of our time including Edwin Hubble, Walter Baade, Fritz Zwicky, Halton Arp and George Abell. They were catalogued by George Abell but naming them Palomar should probably be credited to Helen Sawyer Hogg. The initial list included just 13 clusters with Pal 14 and Pal 15 added later. The reason for their relatively late discovery is that they are very faint due to being either heavily obscured, extremely remote or having few remaining stars. It took the giant 48-inch Schmidt camera at Palomar to discover them.Palomar 13 is one of the smallest and faintest globular clusters known. This is a consequence of its eccentric orbit which brings it close to the galactic centre every 1 to 2 billion years. With each dive through the galaxy, gravitational tidal forces strip away the member stars. Detailed studies offer evidence for a dramatic end to this dwindling cluster's tidal tug of war. Palomar 13's latest close approach was only about 70 million years ago and its next could well turn out to be its last. This image comprises 10 x Luminance (300 seconds each) and 5 x Red, Green and Blue (180, 182 and 145 seconds each), 0.5m f/2.9 ASA Astrograph with FLI ML3200 camera at an altitude of 70 degrees on 10 October 2017. The fields of view are 32’ x 21’ and 18' x 12', respectively.
Hills Observatory: 1 January 2013 to 16 November 2018