Mis à jour : 13 janv. 2020
NGC 869 and NGC 884, also named Caldwell 14 or simply The Double Cluster, are two clusters in the constellation of Perseus. Both are very similar to each other in size, magnitude, and age. Both NGC 869 and NGC 884 are getting closer to Earth at a rate of 24 miles per second.
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. They are a beautiful sight when observed through binoculars or instruments and many individual stars can be resolved if using a large telescope. Each of the clusters contain more than 300 blue/white super-giant stars, many of which are visible in photographs.
We imaged the Double Cluster with our Orion 8" Astrograph and ZWO ASI 1600MM Astrophotography camera. 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.
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 point of needing a Meridian flip and we decided to end it there for the Bubble. Sadly, right after this point, either 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 star clusters. We did not think it would turn out good 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: Orion 8" Astrograph f/3.9
Mount: Atlas EQ-G motorized 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)
LOCATING THE DOUBLE CLUSTER
NGC 869 and NGC 884 can be found 7,500 light-years away in the constellation Perseus. They are very close to Cassiopeia's "W" shape. Both can be seen with the unaided 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 faint stars, and a brighter center in each object.
Represents the jewels from the handle of Perseus’ sword
About twice the size of the Moon
Total mass of at least 20,000 solar masses
PROCESSING OF THE DOUBLE CLUSTER
We imaged the Double Cluster in Perseus with 4 filters:
As with most of our images, we like to show you the stacked image for each individual filter, sadly, these files are lost for this particular target. The Luminance filter was used for longer than the other three as this is where almost all the details come from. The Red, Green and Blue filters are only used to grab the colors for the image.
Processing was very quick and easy. There are no faint gases to show off, and no spiral arms to enhance. The only tricky part about processing the Double Cluster is when making a Star mask. You want to make sure that you play with the settings and run some tests until the stars on the mask are either only background stars or cluster stars, not both.
The Double Cluster is a large, bright and easy target to photograph for any amateur astrophotographers. This is also one of the easiest objects to image for beginner astrophotographers for the Winter months of November, December, January and February.
Although we wish to have spent more time on it, and of course used guiding, we are glad the image turned out as great as it did. Keep an eye out for a Version 2 of our Double Cluster with either a wider telescope or the same instrument but guided and with am expected total exposure time of 2 to 3 hours.
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