Messier 13 (M13) is a large Globular Cluster located in the constellation of Hercules. It is also sometimes known as the Great Hercules Cluster. A globular cluster (GC) is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. The number of stars contained within each one may vary between tens of thousands to many millions of stars. M13 is estimated to contain around 500,000 stars. All the members are in orbit around the gravitational center of the structure. There are over 150 known GC located in our Milky Way galaxy. Globular Clusters are also some of the oldest structures in the galaxy. Most are in the outer regions of the galaxy in the galactic halo with ages ranging from 10 to 13 billion years.
While at first glance most of these GC appear similar, there are unique features within each one. While their apparent sizes vary due to actual size and distance, their concentration also varies greatly. The Shapley-Sawyer Concentration Class is a measurement of their concentration with a range of Class I being the densest and Class XII being the least concentrated. M13 is about the middle of this range, being designated as Class V, Intermediate Concentration. True observations of each GC tend to show unique structures that give each GC its own individuality. Some of these details can be seen in the image I took below at CRO in 2021.
- At high power, hidden within the core, slightly offset from center, there are three subtle dark lanes that join together to form the letter “Y”. This combined effect is nicknamed the M13 Propeller.
- Several streams of stars out from the core that make it appear as Lord Rosse describes as “hairy-looking”, curvilinear branches
Next time when you look at M13, please try and observe these details.
Along with M13, there are a couple of small brighter galaxies that can be seen in this image, The brightest one is NGC 6207 and is located to the upper right in this image. It is also one of the Astronomical Leage’s Herschel 400 objects and is easy to locate and observe with just a moderate telescope. IC 4617 is the smaller edge-on galaxy located about halfway between M13 and NGC 6207.
I just completed gathering and processing data for NGC 6207 from my backyard observatory in Bixby. You can see the final image below.
Next time when you look at M13, please try and observe these details. and objects.
Additional equipment, imaging details and full-size images can be found on my website at:
M13 - Great Hercules Cluster
NGC6207 - Spiral Galaxy
Let me know what you think.
Rod