Updated: Aug 16
Messier 24, also known as the Small Sagittarius Star Cloud, is a large region of sky that is completely filled with stars. This incredible amount of stars overlays the beautiful nebulous background, which I will reveal today.
Object Designation: M24, IC 4715
Also known as: The Small Sagittarius Star Cloud, Delle Caustiche
Object Type: Star Cloud
Distance: 10,000 light-years away
Discovery: June 20, 1764 by Charles Messier
Messier 24 is huge, but is not considered a deep-sky object! It is often captured with a DSLR/Mirrorless camera and lens widefield due to its large size, and the fact that it sits within the bright Milky Way band. In order to reveal the gasses behind the stars (if any), I used a fast telescope under dark skies, and imaged this target for 12.5 hours.
For deep-sky objects to image at the same time this area of the sky is observable, take a look at our list of the 15 best astrophotography targets for summer.
The Sagittarius Star Cloud with a RASA Telescope and No Filters
After many years doing astrophotography, I finally decided to image the M24 star cloud in July of 2023 using my RASA 8 telescope and OSC camera. I had captured M24 in the past widefield when taking Milky Way shots with my DSLR camera, but I had never specifically aimed at this target.
Because of how large M24 is, my focal length of 400mm ended up being perfect, and I simply told NINA to center the field of view on the target and not care about any specific rotation. I spent a total of 12.5 hours imaging this object over several clear nights. This area of the sky goes low in the horizon pretty early so I could only spend about 3 hours on it each time.
The processing, which I will talk about further in this post, was difficult but fun. The result overall came out beautiful, and very impressive as all these gasses are usually hidden behind the stars. If you'd like to try your hand at processing our data yourself, buy our M24 raw data practice files.
Click the image for the full-resolution version!
Want to process your images following our own workflow? Access our PixInsight Guide!
Camera: ZWO ASI2600MC
Telescope: Celestron RASA 8
Mount: 10Micron GM1000 HPS
Total Exposure Time: 15 hours
Exposure Time per frame: 1, 5, and 10 minutes
Utah Desert Remote Observatories
This beautiful picture was taken using our remote telescope hosted in Southern Utah under dark Bortle 2 skies. We have a rig at Utah Desert Remote Observatories, which allows us to shoot on every clear night without setting up in the desert ourselves. For this shot, we replaced our refractor telescope with the RASA 8, and waited for a moonless week to shoot M24. You can get more information on UDRO by watching 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 email@example.com
How to Locate Messier 24
Messier 24 is huge and spans over 9 times the size of the full moon. It is the largest entry in Messier's catalog and the densest concentration of stars in the sky. It is an especially impressive target when observed through binoculars, as more than 1,000 stars can be seen at once in the field of view.
M24 is easily visible to the naked eye when looking towards the Sagittarius region. It is also of course possible to be seen with telescopes, but it truly is best when observed with binoculars.
The best time to observe and photograph Messier 24 is in Summer.
Messier 24 Information
The Sagittarius Star Cloud is located approximately 10,000 light-years away from Earth, and has an apparent size of 1.5 degrees. Its true diameter is 600 light-years across. Messier 24 is a star cloud, so it is not technically considered a deep-sky object. It is simply a dense region of the sky filled with thousands and thousands of stars that look so compact that, back then, it may have looked like a nebula with stars.
The tricky part about imaging Messier 24 is that because of all these stars, the background is almost completely hidden! The image is not very impressive unless you know how to process it well.
I knew that the background must be filled with colorful gasses because M24 is in the bright Milky Way band. Here you can see the star mask, which is a mask of all stars extracted from the image.
It is crazy to think that this star mask almost looks like a regular deep-sky image! Later in this post, we'll talk about how I processed the data to reveal the nebulosity.
Below you can see an annotated version of our M24 image. It shows the nearby NGC and IC objects which are all over the field of view. These are small nebulous objects and star clusters. You can see this in high-resolution on our Astrobin.
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Processing the Sagittarius Star Cloud
Processing Messier 24 was difficult, but so impressive once the stars were removed. The entire time before seeing any nebulosity, I was hoping that I wouldn't mess up the background extraction or apply too much noise reduction, not knowing what was hiding behind all these stars.
I then proceeded to stretch the image and use StarXTerminator, which completely blew my mind. Even though I did expect some bits of nebulosity here and there from some previous research I did, I was shocked to see that the entire field of view was filled with colorful gasses! The incredible number of stars really were hiding all that beauty behind.
Below is what our Master file looked like, it totals 12.5 hours and is what I opened in PixInsight right before starting processing the data. As you can see, once stretched, you can spot a few regions of nebulosity here and there, mostly dark clouds, and one bright red nebula near the bottom right. I never expected to see much more than that behind the stars.
Once the stars were removed, it is a completely new image that popped up on my screen. A colorful, bright, and impressive one that was just begging to be enhanced.
After revealing the details and taking care of the noise, both with RC-Astro PixInsight plugins, I did my best to enhance the dark areas in the dark clouds, play with Curves and the Color Saturation process to enhance the colors throughout the image, and also applied some Local Histogram Normalization to further bring out the fine details.
The image below is what the starless version of the picture looked like before adding the stars back. This is a highly compressed image, but you can still see so many cool shapes of nebulosity all over the image.
I then added the stars back together, and reduced their size so that they wouldn't be too much of a bother when looking at the image overall.
Our Pixinsight Processing Wofklow for Nebulae
If you would like to learn how I process all our images including this one, you can get our PixInsight processing workflow for nebulae HERE.
It includes text lessons, 18 tutorial videos, our custom process icons, and raw data!
As a bonus, you will also find a full walkthrough guide about how to download professional data from NASA and the James Webb Space Telescope!
The file is updated whenever I decide to tweak my workflow or add more to it, and you always get the updates for free!
Messier 24 FAQ
How did M24 get its name?
Messier 24 got the nickname of "Sagittarius Star Cloud" because it is a large region of the sky where thousands of stars are visible, like a blanket of stars, or "star cloud".
In which constellation is M24 located?
You can find Messier 24 in the constellation Sagittarius.
How big is M24?
The Sagittarius Star Cloud has a diameter of 600 light-years. From Earth, it has an apparent size of 1.5 degrees.
How far is M24?
Messier 24 lies approximately 10,000 light-years away from Earth.
How long should my exposure time be when photographing Messier 24?
This will depend on the telescope you have and how dark you skies are. From a Bortle 2 site with our fast f/2 RASA 8, we did 300 seconds which worked great. We probably could have done 600 seconds to divide our number of individual files by 2.
Should I use a filter to image M24?
Messier 24 is best imaged in RGB+HA. It has a lot of hydrogen alpha data, as you saw in our pictures because it lies in the Milky Way band. We personally imaged this target without any filters and used a color camera. At f/2 for 12.5 hours, it gave us enough signal to bring out the Hydrogen alpha without even using an HA filter.
Messier 24 is often considered to be a target that is not so exciting, but it honestly is such an impressive region of the sky if processed properly! This is an easy target for beginners, does not necessarily require filters, can be captured with or without a telescope, and has so much to reveal during processing! What else to ask for?
If you're looking for high-quality astrophotography data to practice your processing skills, our Raw Data page has several datasets for many targets, including this one! These master files have been calibrated and prepared for you to easily open in the processing software of your choice.
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