Mis à jour : 13 janv. 2020
The Bubble Nebula is a beautiful emission nebula discovered by William Herschel in 1787. It lies about 10,000 light-years away in the constellation Cassiopeia. Obviously, NGC 7635 got its nickname from the shape of its expelling gas forming what appears to be a bubble in space. The visible gas is escaping from the center of the nebula, where a star 45 times more massive than our sun lights up its surrounding area.
The photo on the right was taken by the Hubble Space Telescope to celebrate its 26th birthday.
This is, in our opinion, one of the most wonderful images photographed by the orbiting telescope, where you can see a lot of details all over the nebula if you look closely.
We used our usual Orion 8" Astrograph f/3.9 telescope to capture NGC 7635, along with our ZWO ASI 1600MM-Pro CMOS camera. We spent a little over 3 hours on this target then switched to the Double Cluster in Perseus because our telescope got too close to the tripod leg and we were too lazy to do a Meridian flip. The Bubble was also getting very close to Las Vegas' light pollution dome, so we do not regret stopping there.
We did a round of 20 frames for each narrowband filter at 3 minutes each, then launched an additional 10 frames with the Hydrogen-Alpha filter only as it was the one looking the most promising. You can see the result of each filter later in this post.
NGC 7635 is a popular target for amateur astrophotographers, not only because of its beauty but also because it lies very close to a Messier object: the open cluster M52 (left).
We were hoping to be able to also get Messier 52 in the same frame, and even though we could have, we decided not to because we did not want anything to be cut off in our final image.
The test shots we did that included both objects looked perfectly fine, with the Bubble Nebula being on the top left and M52 being on the bottom right, but you should never assume everything will fit just right when it comes to nebulae.
By researching NGC 7635 prior to picking it as our target, we knew that there was a ton of faint gas all around the actual Bubble. If we kept both objects in the same frame, we would have gotten the Bubble itself perfectly, but all the faint gases all around would have been cut off on one side. We'll aim our telescope at M52 and capture it in the near future.
Below is our final image of the Bubble Nebula, with all the acquisition details attached underneath.
NGC 7635 (HaSIIOIII), with the ASI 1600MM
Camera: ZWO ASI 1600mm Pro Mono
Telescope: Orion 8" Astrograph f/3.9
Mount: Atlas EQ-G motorized Mount
Guiding: ZWO ASI 290MM Mini
Acquisition: ZWO ASIAIR
Total Exposure Time: 3 hours and 27 minutes
Exposure Time per frame: 3 minutes
Filters: Ha (1 hour and 27 min) / SII (1 hour) / OIII (1 hour)
LOCATING NGC 7635
The Bubble nebula is located in the constellation Cassiopeia, only 0.5 degrees southwest of Messier 52, its neighboring open cluster.
The easiest way to find this target is to look for Cassiopeia's "W" shape, and simply follow the line going to the Northeast towards Cepheus.
NGC 7635 is very small and not impressive to look at through an eyepiece, but it is a magnificent target to photograph.
It is not a visible object to the naked eye or through binoculars, and using averted vision is recommended even when using a telescope eyepiece because of how diffuse the nebulosity is. Filters may also help, but this is far from being a visually stunning target when looking at it directly.
A large telescope may reveal a non symmetrical bubble shape.
Discovered in 1787
Has a radius of 3 to 5 light-years
Created from a huge young central star’s stellar wind
SINGLE SHOT & PROCESSING OF NGC 7635
We used our three narrowband filters to capture NGC 7635: Ha, SII, and OIII.
Below you can see the stacked images for each filter.
The Bubble Nebula, stacked images for Ha/SII/OIII
Once again, for the majority of emission nebulae, the Ha filter reveals much more details than the other two, as you can see on the left image.
Processing the Bubble Nebula was overall not too difficult. The only tricky part was to make sure to bring out as much of the outer faint gases as possible. This was not easy and it took more than half a day to end up with a final image we liked.
PHOTOGRAPHING THE BUBBLE NEBULA WITH STELLINA
As we were imaging the Bubble with our main telescope, we decided to spend about one hour on the same target with our recently acquired Stellina observation station from Vaonis. You can see the result below taken right from our phone. This image was not processed on our computer and was instead auto-stacked by the software built inside Stellina.
Total Exposure Time: 1 hour
Exposure Time per frame: 10 seconds
NGC 7635 is a small but beautiful object to photograph. It can be difficult to reveal the faint outer gases all around the bubble, but it is a challenge that can be easily accomplished if you are willing to spend several hours imaging this target.
If you own a wide telescope, you will be able to capture two targets at once! Having the Bubble nebula and a Messier open cluster in the same image makes for a fantastic looking astrophotograph. You also do not have to do narrowband imaging on the Bubble nebula, as a regular RGB sensor like the ones found on DSLR cameras can also yield great results. If you are a DSLR camera user and are willing to spend a little bit of money, we would recommend purchasing a DSLR clip-on Ha filter before attempting this target.
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