M23 - Open Cluster In Sagittarius | Astrophotography
Messier 23 is an open cluster in the constellation Sagittarius. It is a great target for astrophotographers as dust from the Milky Way band can be seen all over the background! In this post, you will find information, images, and tips to photograph this beautiful star cluster.
Object Designation: M23, NGC 6494
Also known as: The Sagittarius Cluster
Constellation: Sagittarius
Object Type: Open Cluster
Distance: 2,150 light-years away
Magnitude: 5.5
Discovery: Charles Messier in 1764
Messier 23 is an easy target for beginner astrophotographers, although as you will see below, there is a lot of dust to reveal in the field of view, which might require some advanced techniques to get the best possible result.
Messier 23 gets high in the northern sky in July and so it is best photographed in the Summer season.
Messier 23 Astrophotography with IFN and other Gasses
July 2023
I wanted to spend a long time on this target, at least 20 hours, because I knew that there would likely be plenty of Milky Way dust in the background. I chose to spend 23 hours on it, simply because it has the designation M23.
I am glad I spent this much time because as you can see, we got so much going on all over the field of view that the cluster itself is almost difficult to see! This was taken with a fast RASA 8 from the Bortle 1 skies of Astronomy Acres in New Mexico.
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: 23 hours
Exposure Time per frame: 300 seconds
Filters: N/A
Gain: 100
How to Find the Messier 23 Cluster
Messier 23 is located in the constellation Sagittarius. It lies in a rich region of the Milky Way, making it a beautiful cluster to observe and photograph. Finding M23 is relatively straightforward by star-hopping.
To locate Messier 23, first identify the Teapot asterism in Sagittarius. Start at the top of the Teapot and move north to the star Mu Sagittarii. From there, hop approximately 1.5 degrees west to reach Messier 23.
Messier 23 has an apparent size of 27 arc minutes, and its brightness makes it visible through binoculars or a small telescope. With binoculars, the cluster appears as a hazy patch, while a telescope will reveal individual stars, especially with higher magnifications.
Messier 23 is in the same region of the sky as other notable Messier objects, including the Lagoon Nebula (M8) and the Trifid Nebula (M20).
The best time to observe and photograph M23 is in Summer.
M23 Cluster Information
Messier 23 is one of the several open clusters in the constellation Sagittarius, and has an estimated age of about 220 million years. For comparison, our Sun is about 4.6 billion years old, making M23 rather young.
M23 contains around 150 members, including many bright, young stars.
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The Gasses Behind M23
Messier 23, like several other objects in the Summer sky, lies within the bright Milky Way band. This means that spending enough time on the target will likely show the Milky Way dust all around, especially from a dark site!
I especially like going deep on clusters like this one because these are often shown against a black background, whereas there is so much gas begging to be revealed.
The screenshot above shows the M23 cluster's location as viewed from a planetarium software (in this case, SkySafari). You can clearly see that it sits on the colorful gasses of the Summer Milky Way band.
Processing M23
Messier 23 is easy and fun to process! Easy because it is an open cluster, so you are technically just processing stars that are far appart from each other. Fun because if you want to, you have the choice to try to reveal as much of the faint background gas as possible in your shot. This is similar to what you would do if you were to process a dim nebula, and so you will need to be careful with the histogram levels and noise in order to get a good result.
Here you can see what a 300-second single shot looks like. As you can see, the cluster is visible, and the dark dust lanes within the Milky Way band also show up easily, especially on the left side!
If you'd like to learn how to process your images, get our astrophotography processing guides! They include written and video lessons, raw data, and straight to the point tips to help you get the best out of your images.
Messier 23 FAQ
In which constellation is M23 located?
You can find Messier 23 in the constellation Sagittarius.
How big is M23?
M23 has a diameter of approximately 15-20 light-years. From Earth, it has an apparent size of 27 arc minutes.
How far is Messier 23?
M23 lies approximately 2,150 light-years away from Earth.
How long should my exposure times be when photographing M23?
We did 300 seconds (5 minutes) which is a good place to start if you're aiming to get both an open cluster and background dust. You can increase this to 10 minutes or more depending on the telescope you use and how dark your skies are! If you only care about getting an easy picture of just the stars with a featureless background, then feel free to take 30-sec shots.
Should I use a filter to image M23?
A broadband filter might help enhance the contrast and reduce light pollution if you are imaging from the city, but we wouldn't recommend using one. If you are imaging from a dark site, you will not need a filter since M23 is an open cluster and is just stars! If your main goal is to capture the faint gasses in the background, you could always try using an HA filter to see if any of this dust includes hydrogen alpha. With our RASA and no filter, we did not see any areas rich in HA in that field of view.
Final Thoughts
Messier 23 is a fun and easy target in the Summer sky. Sure, there are many more exciting objects to capture around the same area during the Summer months, but you can also find excitement in M23 by going deep and revealing all the beauty in the background!
Have you imaged the M23 cluster? If so, upload your picture in the comments! We'd all love to see your work :)
Clear Skies,
Galactic Hunter
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