M15 - The Pegasus Globular Cluster With IFN | Astrophotography
Updated: Jun 8
Messier 15 is a large and bright globular cluster in the constellation Pegasus, and is also one of the densest clusters in our galaxy. M15 is one of just four globular clusters to be home to a planetary nebula, named Pease 1. In this post, you will find information, images, and tips to photograph this beautiful star cluster.
Object Designation: M15, NGC 7078
Also known as: The Pegasus Globular Cluster
Constellation: Pegasus
Object Type: Globular Cluster
Distance: 35,700 light-years away
Magnitude: 6.2
Discovery: Jean-Dominique Maraldi in 1746
Messier 15 is an easy target for beginner astrophotographers, although as you will see below, there is so much more to reveal than just the stars from the cluster if you put some work into it! This makes M15 a fantastic object for both beginner and advanced astrophotographers.
Messier 15 Astrophotography with IFN and other Gasses
October 2023
I added M15 to my imaging sequence as a gap-filler between two galaxies. Despite knowing that this was one of the best globular clusters to observe visually, I didn't expect much from it photography-wise, so only imaged it for a total of three hours doing 30-second exposures.
While processing the data, I noticed some faint IFN in the shape of an "L", and immediately went to check Astrobin to see if it was captured before. The answer was yes, it had been captured a few times, and that excited me to spend more time on the cluster. I accidentally trashed the three hours of data I already had on it while making space on my hard drive, and just decided to start from scratch doing 5-minute exposures. My hope was to not only reveal all of the IFN, but also get more from the background. I was not disappointed while processing the data after 14 hours on it!
Be sure to scroll down to learn more about all the IFN, and the other gasses present in the image.
Click the image for the full-resolution version!
GEAR USED:
Camera: ZWO ASI2600MC
Telescope: Celestron RASA 8
Mount: 10Micron GM1000 HPS
Guiding: ZWO ASI 220MM Mini
Accessories: Celestron Focuser / PrimaLuceLab Eagle 5S
Processing: Pixinsight, with R-C Astro plugins. Final touches in Skylum Luminar Neo
ACQUISITION DETAILS:
Total Exposure Time: 14 hours
Exposure Time per frame: 300 seconds
Filters: N/A
Gain: 100
How to Find the Messier 15 Cluster
M15 is located at the edge of the large constellation of the flying horse, Pegasus. It is very close to the Delphinus and Equuleus constellations, and is not too difficult to find by star-hopping.
To find Messier 15, look up to first spot the large Pegasus square. From there, hop to the two bright stars going away from the square towards Aquarius, then make a 90-degree left turn to the next bright star. You should now be on Epsilon Pegasi, which is the brightest star in the constellation Pegasus. M15 can be found just 4° WNW beyond this star.
M15 has an apparent size of 18 arc minutes, and is just bright enough to be spotted with the naked eye if you are observing from a perfectly dark location. Through binoculars, the cluster will look like a fuzzy white star and you will need a large telescope to be able to resolve individual stars.
Messier 15 is not far from another globular cluster in the Messier catalog: Messier 2.
The best time to observe and photograph M15 is in Fall.
M15 Cluster Information
M15 is one of the oldest globular clusters known, with an age of about 12 billion years old! For comparison, our sun is just 4.6 billion years old. The stars within M15 started forming at the very beginning of the creation of our Milky Way.
Talking about stars, M15 contains more than 100,000 of them, making it one of the densest globular clusters in our galaxy. Some notable stars in M15 are 112 variable stars, 8 pulsars, and one double neutron star system named M15-C. It is also home to a planetary nebula, which we'll cover later.
M15 by NASA
The image below was released by NASA and ESA on November 14, 2013. It shows the beautiful M15 cluster photographed by the Hubble Space Telescope using the Wide Field Camera 3 and Advanced Camera.
Blue stars are very hot, while yellow stars are much cooler. You can see how packed and bright the center of the object is.
Two surprising discoveries were made by scientists studying Messier 15: a planetary nebula, which we'll talk about next, and a rare type of black hole in the core of the cluster.
Pease 1, the Planetary Nebula Within M15
Pease 1 is a planetary nebula located within Messier 15. It was discovered in 1927 when Francis Gladheim used a 100-inch Hooker reflector telescope at Mount Wilson Observatory to take a picture of the cluster.
Pease 1 was the first planetary nebula to be found inside of a globular cluster. Since then, only three other planetary nebulae have been found inside of globular clusters and confirmed to be gravitationally bound to them.
Visually, it is possible to observe Pease 1 with a large telescope and the use of an OIII filter, but it is very challenging and requires a sky void of any light pollution.
The other three planetary nebulae found inside of globular clusters are:
Messier 22
NGC 6441
Palomar 6
The planetary nebula visible by Messier 46 does not make this list as it is believed to simply be located in our line of sight between Earth and M46, and not gravitationally bound to the cluster.
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The Hidden Gasses Behind M15
The main exciting part about our amateur astrophotography image of M15 is all the faint gasses (or mostly dust to be scientifically correct) present in the background.
Most pictures of M15 show the bright globular cluster with a pitch-black background, so it is interesting to have a different view of this object and see all of the hidden beauty behind it.
Hydrogen Alpha in M15
Although I expected to see a lot of IFN after checking Astrobin, I didn't expect to see any hydrogen alpha gas by the cluster.
This was a nice surprise, and it looks almost as if the red HA gas is flaming out of the cluster. Note that the photo attached here was rotated so that the HA is on top, but it is on the right side on our original pic!
It also seems like the dust on the left side is being lit up by the bright blue star nearby, which could technically make that dust some type of reflection nebula?
Or... it might just be an overprocessed region while trying to bring out the IFN all over the image.
IFN around M15
IFN stands for Integrated Flux Nebula. These are composed of mostly dust particles, with hydrogen, carbon monoxide, and a few other elements. They are technically not nebulosity, but rather just space dust. Unlike nebulae, IFN dust is not get illuminated by specific stars but instead by the integrated flux of all of the stars in our galaxy. This is what makes IFN so faint and difficult to image. They not only require a very dark sky far from any light pollution to be visible in photographs, but also hours of total exposure time.
IFN is mostly present at high galactic altitudes, both to the north and the south celestial poles.
As you can see on this screenshot taken from SkySafari, M15 is located very south of our Milky Way galaxy plane, where IFN is likely to be present.
Annnnnnd our image shows a ton of IFN! The most interesting part in my opinion is the shape of the IFN dust going around the cluster in an "L" or "S" shape. It makes a perfect 90-degree turn to go around M15 and continues its way to the other side.
Several galaxies are also visible in the background as an added bonus! You can see the starless version below which shows the full extent of the IFN.
IFN is present around some other popular deep sky objects, such as:
How to Process M15 with IFN
Processing this cluster is normally very easy, unless you're on a mission to reveal as much IFN as possible like I was.
I decided to process this image live on YouTube, and you can access the video if you're a member supporting our channel. The livestream lasted one hour, I answer your questions while processing the data, and get a nice result at the end! I did keep working on the image a little after the stream was over until I was fully satisfied with the result.
We also have some premium "follow-along" guides you can access if you need to learn new ways to process your images.
The best guide to follow for this specific case would be our advanced Nebula processing guide, as the techniques used for the nebula are similar to the ones you can use for IFN. The guide has 20 lessons, walkthrough tutorial videos, custom pre-sets for your PixInsight dashboard, and raw data.
Utah Desert Remote Observatories
We used our RASA 8 telescope and OSC camera installed at Utah Desert Remote Observatories to capture the M15 cluster. It is so nice to have an astrophotography rig at a remote observatory under beautiful Bortle 2 skies as it allows us to spend many hours on the object of our choice without having to drive out to the desert, set up our gear and pack up several times.
If you want to learn more about remote observatories and UDRO in general, be sure to watch the video below!
If you would like to permanently host your telescope next to ours under amazing desert skies, you can contact the owner at info@utahdesertremote.com
Messier 15 FAQ
In which constellation is M15 located?
You can find Messier 15 in the constellation Pegasus.
How big is M15?
M15 has a diameter of 176 light-years. From Earth, it has an apparent size of 18 arc minutes
How far is Messier 15?
M15 lies approximately 35,700 light-years away from Earth.
How long should my exposure times be when photographing M15?
We started with 30-second exposures, which is usually what we recommend for globular clusters as the stars are very packed and taking longer exposures means risking trashing several frames in case of wind of tracking issues. Once I realized that there was IFN, I decided to take 300-second exposures instead and only kept the frames that had been tracked perfectly. Long exposures are required for IFN.
Should I use a filter to image M15?
The stars in M15 and the IFN do not require a filter. If there truly is some HA around the cluster as our image shows, then using an HA filter as well could be a good idea!
What equipment do I need to photograph Messier 15
You can photograph Messier 15 with pretty much any telescope. The size of the instrument you plan to use depends on what exactly you aim to capture. You can either use a large telescope and get a close-up shot of the cluster, or use a smaller instrument and get a wide-field view of the object which will allow you to include the IFN.
The telescope we used is the RASA 8 which has a focal length of 400mm. The RASA was very helpful in our mission to get the IFN because of how fast it is at f/2.
Final Thoughts
Messier 15 is one of these often-underrated objects just because it is a globular cluster. I am very happy to have been able to notice the slight IFN on my original shots, researched similar pictures online and decided to go way deeper on it. Despite the overall "overprocessed" look of the final image, it was a fun challenge to do my best to reveal as much IFN as possible, and the surprise Hydrogen Alpha!
Have you imaged the M15 cluster? If so, upload your picture in the comments! We'd all love to see your work :)
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