Now I know what David Bowman saw and felt, as he travelled through the star gate in 2001: "My god, it's full of stars"

While M13 is an "easy" photographic target due to its’ brightness, obtaining good resolution of its densely packed core is a challenge, as there are some 100,000 stars. The density in the core is about 100 times that in our sun's neighborhood, such they can interact with each other--even sometimes collide. Since the stars in the cluster were formed together, and the cluster is over 11 billion years old, they should all be the same age--old. So why do we see blue stars, which have short lives? The blue stars we see here are Blue Horizontal Branch (BHB) stars, which are about 1 magnitude brighter than blue stragglers (which are main sequence stars that have gained extra mass due to stellar interactions), and far more numerous in a low-metallicity cluster like M13. BHB stars are the natural evolution of post-red giant branch single stars, after the "helium flash" occurs at the tip of the red giant branch. Essentially, they can be considered "helium main sequence" stars. Thanks again to Ray Butler for his help understanding the blue stars in globular clusters--any errors in my interpretation here are my own.

Why HOO for a globular cluster? It started around full moon and in my Bortle 8, I felt I couldn’t lose by using my LeNhance NB filter for an HOO image with my CMOS color camera, to reduce sky glow. I also found previously that my stars were way less bloated with the filter, so again a good thing for a closely packed globular cluster. Then I got hooked, every night I took more exposures and saw more and more fainter stars. I'm still unhappy I stopped after all these hours, I definitely will have to add more data next year.

Finally, on that note of more data, please take a look at the crowd sourced image with nearly 273 hours of combined integration from Morton Balling—it is David Bowman all over again and again!