Celestial hemisphere:  Northern  ·  Constellation: Hercules (Her)  ·  Contains:  Hercules Globular Cluster  ·  IC 4617  ·  M 13  ·  NGC 6205
Messier 13, Rick Veregin
Messier 13
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Messier 13

Messier 13, Rick Veregin
Messier 13
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Messier 13

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Description

While M13 is an "easy" photographic target due to it's brightness, obtaining good resolution of its densely packed core is a challenge. Messier himself was convinced that this was only a nebula, and that there were no stars in M13. It was 65 years later to prove him wrong. The apparent count of stars is 100,000, though one hopes no astronomy students lost their minds counting them. The density in the core is about 100 times that in our sun's neighborhood, such they can interact with each other--even 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 stars, which are about 1 magnitude brighter than blue stragglers, and far more numerous in a low-metallicity cluster like M13. They 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 to Ray Butler for his help understanding the blue stars!)

To help with resolving the stars, I used a 3X drizzle in DSS. I could have done with some good seeing too, but very rare for my location.

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