Messier 13 – The Great Globular in Hercules

A very popular astrophotography target, Messier 13 (M13) is one of the largest and brightest globular clusters one can apprehend from the Northern Hemisphere.

English astronomer Edmond Halley (of Halley’s Comet fame) discovered M13 in 1714. The stars in M13 are packed 100 times more densely than the stars in our neighborhood. The stars are so close together, that sometimes they actually collide, which can create a new star called a blue stragglers. Blue stragglers are stars in an old cluster that appear brighter and bluer than we would expect given the cluster’s age.

Globular clusters are ancient. They are many billions of years old—usually 10 to 13 billion years old—almost as old as the universe itself. The stars they contain tend to be very old as well, because star formation inside the cluster has largely ceased. The formation of globular clusters is not well understood. Current research leans toward the idea that they formed from very dense molecular clouds in the early universe. Some larger globular clusters may once have been dwarf galaxies whose larger star populations were stripped away from the core by larger galaxies.

One thing that makes M13 unique is the three-bladed “propeller” feature near its core. This feature is caused by a lesser density of stars in the three “blades” of the propeller. Here’s a crop showing an exaggerated version of this feature at eleven o’clock near the core:

When I got my first imaging telescope, a Celestron 1100 EdgeHD in June 2020, the first deep-sly target I went after was M13. The result is nothing to write home about, but I was absolutely thrilled by it at the time:

M13 Facts

Distance: 24,100 light years

Number of stars: 300,000 to 500,000+

Diameter: 145 light years

Age: 11.7 billion years