What is the M13 Hercules Globular Cluster?
The Hercules constellation is home to a fascinating celestial object known as M13 or Messier 13, also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules, the Great Hercules Globular Cluster or the Hercules Globular Cluster.
M13 The Hercules Globular Cluster is about 22,000-25,000 light-years away from Earth. This globular cluster is one of over one hundred that orbit the center of the Milky Way.
The Hercules Globular Cluster is one of the brightest and largest globular clusters in the Northern Hemisphere. It is composed of several hundred thousand stars, forming a compact and spherical shape.
In 1714, a notable English astronomer and mathematician named Edmond (or Edmund) Halley made the important discovery of M13. He was the first person to calculate the orbit of a comet, which was subsequently named after him. Additionally, on June 1, 1764, another astronomer named Charles Messier, cataloged M13 into his list of celestial objects called Messier’s list, later known as the Messier Catalogue.
M13's age and size
The age of M13 The Hercules Globular Cluster, estimated to be around 12 billion years old, suggests that it formed early in the universe’s history. Its size, spanning 145 light-years in diameter, makes it one of the largest globular clusters in our galaxy.
Number of stars and stellar density in M13 The Hercules Globular Cluster
The Hercules Globular Cluster contains a staggering number of stars, with estimates ranging from 300,000 to over 500,000. This high stellar population is what gives the cluster its luminous appearance and makes it a prime target for study.
In the vicinity of the central part of this cluster, the concentration of stars is approximately a hundred times higher compared to the density around our sun. The proximity of these stars sometimes leads to collisions, resulting in the formation of new stars. These newly formed stars, known as “blue stragglers”, appear to be younger than the surrounding stars and are of significant interest to astronomers for scientific research.
What Are The Other Objects Surrounding M13 The Hercules Globular Cluster?
Located near Messier 13 is NGC 6207, an edge-on galaxy with a magnitude of 12 (not visible in the field of view in my astrophoto below). It can be found 28 arcminutes directly northeast of M13. Positioned between NGC 6207 and M13 is a small galaxy known as IC 4617 (see astrophoto below of M13 with annotations), situated north-northeast of the center of the large globular cluster. When observed at lower magnifications, the cluster is flanked by two stars with a magnitude of seven, HIP 81848 and HIP 81673 (see astrophoto below, M13 with annotations). HIP 81848 is an orange/red star which is cooler and older than the younger and hotter star, HIP 81673. You can notice that HIP 81673 is younger because it is blue-white colored. HIP 81673 is also hotter than our own star, the Sun, which is white.
Similar targets like M13 The Hercules Globular Cluster are the M92 Globular Cluster and the NGC 6229 Globular Cluster.
Another object is NGC 6058, an often overlooked planetary nebula, but it is really faint. It has a visual magnitude of 12.9 and you’ll need a telescope with an aperture of at least 10 inches (250mm) or more. Using a UHC filter will also make it easier to observe this small planetary nebula and reveal more structure.
Observing and Photographing M13 The Hercules Globular Cluster
The Hercules globular cluster is most easily observed during the spring and summer months in the Northern Hemisphere from latitudes greater than 36 degrees north when the constellation Hercules is high in the night sky. Additionally, finding a location with minimal light pollution is crucial for optimal viewing conditions. Away from the bright city lights, rural areas or high-altitude locations offer the best chance to appreciate the beauty of the Hercules Globular Cluster fully.
You can easily find M13 between the bright stars Vega and Arcturus during spring and summer in the Northern Hemisphere.
With an apparent magnitude of 5.8, it’s barely visible with the unaided eye on clear nights. M13’s diameter is about 23 arcminutes (about 2/3 the diameter of the full moon) and it is easily viewable in small telescopes. Telescopes with an aperture of at least four inches can resolve stars in the outer extent of M13. However, you’ll need a larger telescope that gathers much light, an 8- or 10-inch, to resolve the stars into the center of the cluster.
Messier 13 can be spotted with a pair of binoculars. The Hercules globular cluster appears as a small, circular, hazy glow. I have observed M13 several times with my 10x50mm binoculars. It is a beautiful sight, I can assure you. The first time I saw M13 with a pair of binoculars, I did not know at all that I was looking at Messier 13 :-D, I was overwhelmed by this beautiful globular cluster (see also my blog post about “Observing and photographing” M34 Open Cluster: https://beatriceheinze.com/portfolio/m34-open-cluster-in-perseus/ ).
Later I also observed M13 once with my 8″ Newtonian telescope but with a pair of binoculars, you still get that beautiful 3D effect.
Astronomical observations have shown that the Hercules globular cluster contains a rich mix of stars, ranging from old, metal-poor ones (yellow/orange colored stars, see my astrophoto of M13 below as an example) to younger, metal-rich ones (blue colored stars, see my astrophoto of M13 The Hercules Globular Cluster (heavy crop) below as an example). By incorporating this knowledge into your photography, you can create visually stunning images that showcase the diverse nature of this celestial marvel. So, before embarking on your astrophotography journey, take the time to learn about the target object and its stellar populations. This will undoubtedly elevate the quality of your photographs and allow you to capture the true essence of the Hercules globular cluster.
Astrophotography
I took the image at the top (below the cropped version) with my 8″ Newtonian telescope without using any filter. This 8″ reflector telescope increases the clarity of individual stars closer to the center. Resolving the bright core into stars is still difficult and seems therefore a “Herculean task” :-). Photographing M13 the Hercules Globular Cluster without using a filter in a Bortle 6 zone and shooting with 30-second exposures, can already give great results and keep the stars in a more beautiful, natural-looking way. You can easily distinguish the golden, and yellow stars from the blue ones. I used a dedicated astro camera (one-shot color), the ZWO ASI 294MC Pro.
To capture clear images of globular clusters such as M13, it is crucial to have stable atmospheric conditions, precise focus adjustment, reliable tracking, and autoguiding.
However, the data for my astrophoto below (heavy crop) and at the very top were taken without autoguiding and when the sky was not so stable.
Image details
- Telescope: Sky-Watcher Explorer BD N200/1000
- Mount: iOptron CEM60
- Camera: ZWO ASI 294MC PRO
- Telescope control: ZWO ASIair v1
- Software: Astro Pixel Processor; Affinity Photo (Logo) & DPP4 (little finishing touch)
Data captured on 06/03/2021
(image all the way at the top: original view // image here above “Image details”: cropped version)
Total integration time: 3,5 hours
SQM-L: 19.34 (Bortle 6)
No coma corrector, no filter, no guiding.
Conclusion
The M13 Hercules Globular Cluster is undeniably one of the most captivating objects in the night sky. Its rich history, scientific significance, and stunning visual appeal make it a favorite target for astronomers and amateur stargazers alike. Whether you’re a seasoned observer or just beginning your journey into the wonders of the universe, M13 is a must-see night sky jewel that will leave you in ‘awe’ of the cosmos.
