NGC 869 and NGC 884, also named Caldwell 14 or simply The Double Cluster, are two clusters in the constellation Perseus. Both are very similar to each other in size, magnitude, and age. This bright pair of clusters is a great astrophotography target for beginners. In this post, you will find information, images, and tips to photograph The Double Cluster in Perseus.
Object Designation: NGC 869 and NGC 884, Caldwell 14
Also known as: The Double Cluster in Perseus
Object Type: Open Clusters
Distance: 7,460 and 7,640 light-years away
Magnitude: 3.7 and 3.8
Discovered in: Hipparchus, 130 BCE
The Double Cluster is bright and large, making it an easy target using any type of telescope and camera. We have imaged the two open clusters several times since starting astrophotography, and will show you our main attempts below!
The Double Cluster with a Refractor Telescope and Monochrome Camera
This is our first light after setting up our 5" refractor telescope at a remote observatory in Utah!
We'll talk about this more in-depth later in this post for those of you interested in installing your telescope under a dark sky permanently.
The Double Cluster in Perseus is most of the time captured in RGB, but a few widefield images on the internet show a considerable amount of hydrogen alpha gas all around the two objects. I wanted to focus entirely on revealing as much HA as possible in this image, and it turned out awesome!
I spent one night capturing R, G, and B data. Then I spent 3 extra nights (20 hours) imaging but this time with a hydrogen alpha filter. Even with 20 hours of exposure in HA, it was difficult to bring out the gas during processing because it is still relatively faint in this area of the sky. Below is what I was able to achieve. You can see the beautiful Double Cluster and an incredible amount of HA gas behind and around. There are some tilt issues, but after countless nights trying to fix it, I'm now trying not to think about it as tilt keeps ruining my sanity.
Want to process your images following our own workflow? Download our PixInsight PDF Guide!
Telescope: Stellarvue SVX130
Mount: 10Micron GM1000 HPS
Guiding: ZWO ASI 290MM Mini
Accessories: Moonlite Nitecrawler focuser / Pegasus Astro Ultimate Powerbox
Processing: Pixinsight, with RC-Astro plugins
Total Exposure Time: 22.5 hours
Exposure Time per frame: 50 minutes each for R, G and B, 20 hours for HA
Filters: Chroma 3nm H/S/O
The Double Cluster with a Beginner Reflector Telescope
Our very first attempt at imaging the Double Cluster was in 2019, using our 8" Newtonian Astrograph and ZWO ASI 1600MM astrophotography camera. Back then, we said that we'd like to one day re-visit this target with a wider telescope, and do our best to frame a third star-cluster in the frame: NGC 957. It seems like we still haven't included this cluster in our latest image!
NGC 957 is much smaller and really isn't that impressive looking, but it is always nice to add an extra deep sky object in your image if you can!
We imaged the Double Cluster after spending three hours on the Bubble Nebula (NGC 7635). We decided to switch to this new target because our telescope was reaching the Meridian and was about to do a Meridian flip, so we decided to end it there for the Bubble. Sadly, right after this point, our guiding decided it was done for the night and refused to work. We had no choice but to image this target unguided.
Thankfully, we did not plan to take exposures longer than 30 seconds anyway as this is what we usually do for dense star clusters. We did not think it would turn out well so we spent less than half an hour on it. We kind of wish we kept going though as the image below is just 25 minutes of total exposure and doesn't look too bad!
NGC 869 & NGC 884 (LRGB), with the ASI 1600MM
Camera: ZWO ASI 1600mm Pro Mono
Telescope: 8" Newtonian
Mount: Motorized Equatorial Mount
Guiding: None (Did not work!)
Acquisition: ZWO ASIAIR
Total Exposure Time: 25 minutes
Exposure Time per frame: 30 seconds
Filters: L (10 minutes) / R (5 minutes) / G (5 minutes) / B (5 minutes)
How to Locate the Double Cluster in Perseus
NGC 869 and NGC 884 lie respectively 7,460 and 7,640 light-years away in the constellation Perseus. The pair of clusters is located very close to Cassiopeia's "W" shape, and people sometimes assume that the Double Cluster is in Cassiopeia.
The best time to capture the Double Cluster is in Fall. NGC 869 and NGC 884 are always above the horizon throughout the year, so you can tackle them any time as long as they are high enough from your location!
With an apparent size of 30' and magnitudes of 3.7 and 3.8 respectively, NGC 869 and NGC 884 are bright enough to be spotted with the naked eye and are usually easy to find if you are observing from a dark location.
The Double Cluster can be spotted in the middle of an imaginary line that links the Cassiopeia star Ruchbach, and the star Miram in the constellation of Perseus.
Looking at the double cluster through binoculars is a beautiful sight, with both clusters of stars looking like two worlds dancing together. A telescope will reveal an immense number of individual stars and a brighter center in each object.
The Double Cluster in Perseus Information
The Double Cluster lies in the Perseus arm of our Milky Way galaxy. Both clusters are young when compared to most other cluster groups, and are believed to be about 14 million years old. The Double Cluster is home to hundreds of young stars, including 300 blue-white supergiant stars in each object. Besides the stars within, the Double Cluster is also surrounded by a halo of stars, which altogether have a total mass of 20,000 solar masses.
NGC 869 has a mass of 4,700 solar masses, while NGC 884 has a mass of 3,700 solar masses. Both clusters are getting closer to Earth at a rate of 24 miles per second.
Above you can see two pictures, the top left one is a ground-based image of the Double Cluster. The one on the right is a section of the Double Cluster photographed by the Hubble Space Telescope.
This image was taken using the Wide-Field and Planetary Camera 2 installed on the HST, with a single visible-light filter processed in Blue. Because of the long focal length, the Hubble Space Telescope could not capture the whole Double Cluster, so instead photographed a small portion of NGC 884. A fun fact about this image is that the Hubble Space Telescope was actually busy imaging a different target, and used its free camera to capture this as a parallel observation.