M13, also known as the Hercules Globular Cluster, is one of the most prominent and well-studied globular clusters in the northern sky. Here are its main characteristics:
General Description- Location and Visibility: M13 is located in the constellation Hercules
- Distance: It lies approximately 22,200 light-years away from Earth
- Apparent Magnitude: The cluster has an apparent magnitude of 5.8
Structure and Composition- Diameter: M13 spans about 145 light-years in diameter.
- Core: The cluster has a dense core with a radius of about 1.7 light-years.
- Star Population: It contains several hundred thousand stars, with estimates ranging up to around 300,000 stars.
- Metallicity: M13 has a relatively low metallicity (about [Fe/H] = -1.53), indicating it is composed mainly of older, metal-poor stars. This low metallicity suggests that the cluster formed early in the history of the galaxy, before many of the heavier elements had been synthesized in stars.
- Age: The cluster is approximately 11.65 billion years old, indicating it is an ancient formation from the early universe.
Stellar Composition- Star Types: M13 is rich in various types of stars, including:
- Red Giants: Numerous evolved stars that have left the main sequence and expanded.
- Horizontal Branch Stars: Stars that are burning helium in their cores and are found in the horizontal branch phase of stellar evolution.
- Blue Stragglers: These are more massive and bluer than the cluster's other stars, likely formed through stellar collisions or binary mergers.
- Variable Stars: M13 contains about 19 known RR Lyrae variable stars.
Personal notesM13 belongs to the category of objects I wanted to immortalize only with an appropriate setting and upon mastering of the processing. As a matter of fact, despite its strong brightness, this very peculiar object is not the typical low hanging fruit to start astrophotography. In particular, the very high stellar core density requires multiple masks enabling to still observe the smallest stars, as well as their color within the core without dimming the very interesting external region of the cluster. I must admit that, depending on how the masks are applied, one can “shape” the cluster in a very personalized manner, which was not my purpose. So, I tried to keep the original structure of M13, which is a very dense core within a larger and dimmer structure. I artificially added a cosmetic spike on HD150679 as an “artistic” touch.
As usual don’t hesitate to provide constructive feedback.
CS,
Nicola
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