What is The M92 Globular Cluster?
The M92 Globular Cluster (also known as Messier 92, M92, or NGC 6341) is a beautiful and impressive collection of about 330,000 stars that you can find in the northern constellation of Hercules. The cluster is about 27,000 light-years from Earth and has an estimated total mass of about 330,000 solar masses. The diameter of Messier 92 is 109 light-years. It was first observed by German astronomer Johann Elert Bode on December 27, 1777. Charles Messier rediscovered it on March 18, 1781. William Herschel first resolved the individual stars in M92 in 1783.
Messier 92 is an Oosterhoff Type II (OoII) Globular Cluster (which means a metal-poor cluster) and is one of the most famous globular clusters in the night sky. Maybe not as popular as M13 the Hercules Globular Cluster, also located in the Hercules constellation (of course :-)), but that doesn’t mean that the M92 Globular Cluster is less beautiful. It’s only not as bright in the core as Messier 13.
What makes The M92 Globular Cluster so special?
M92 consists mainly of hydrogen and helium. That’s why it belongs to a group of metal-poor clusters (Oosterhoff Type II globular cluster (OoII)). Among astronomers, all elements heavier than hydrogen and helium are called metals.
The M92 Globular Cluster is one of the oldest global clusters in the northern sky. The estimated age of M92 is 14.2 billion years. Almost the same age as the universe itself!
Additionally, it contains variable stars of the RR Lyrae type (periodic variable stars). RR Lyrae variables are some of the most luminous stars in the sky. They vary greatly in brightness (fluctuation or pulsation), with some being much brighter than others. This variation is likely due to several factors, including luminosity, mass, and temperature. This variability allows astronomers to study its dynamics and learn more about how these types of stars die.
What are some of the best ways to view The M92 Globular Cluster?
M92 is a globular cluster located north of the equator, which makes it visible from (most parts of Earth year-round). However, it is best viewed during summer evenings when it is high in the sky.
M92 can be seen with the naked eye under very good viewing conditions.
It is a fairly easy object to find with a small telescope, and it contains many interesting stars including some double and multiple stars. Through a small telescope, M92 can be seen as a faint, nebulous smudge even in light-polluted skies. In dark sky conditions, it can be further resolved and especially if you use a telescope, like an 8″ Newtonian or bigger for example.
The M92 Globular Cluster can be viewed using several telescopes, including a Schmidt-Cassegrain telescope. You can also view it using your webcam or smartphone. Messier 92 is a bright cluster with an apparent magnitude of 6.4.
Viewing M92 through 10×50 binoculars is also a treat for your eyes. I always like to use my 10×50 binoculars to observe clusters like the M92 or the M44 Beehive Cluster.
Astrophotography
Although it’s best to photograph M92 in the summer, especially in July here in Belgium, I already photographed it beginning in June 2021.
I used my 8″ Newtonian telescope with the one-shot-color (OSC) camera ZWO ASI294MC Pro attached to it. No filter came into play. I wanted to keep the star colors as natural as possible. The only downside to it is, that a halo has formed around the bright red star in the right corner above due to the lack of a UV-IR filter, as you can see in my astrophoto. The ZWO ASI294MC Pro camera has only an AR protection window (anti-reflective protection window).
But besides the halo around the bright red star, I’m overall quite pleased with how the picture came out. And especially for such an amount of exposure time: only a bit more than 2 hours. 263 frames with an exposure time of 30 seconds each were used.
This year I did not get the occasion to photograph M92 again, so I could add more data to my current one. Let’s hope for next year :-).
Image details
- Telescope: Sky-Watcher Explorer Black Diamond N200/1000
- Mount: iOptron CEM60 on an iOptron tri-pier
- Camera: ZWO ASI294 MC Pro
- Filter: No filter
- Telescope control: ZWO ASIair Gen.1
- Software: Astro Pixel Processor (stacking & processing); PixInsight (little post-processing: SCNR -> Degreen)
No guiding, no coma corrector
Data captured in the nights: 02/06/2021 & 10/06/2021 => Total exposure time: 2.19 hours
SQM-L average): 19.12 => Bortle class 6 (Bright Suburban Sky)
The M92 Globular Cluster is a luminous treasure that you may want to add to your list of favorite celestial sights. It’s an interesting and unique object that you won’t want to miss.
