NGC 7635 – The Bubble Nebula
The Bubble Nebula (NGC 7635) is an HII region in the constellation Cassiopeia. Its iconic “bubble” shape was created from the stellar wind created by the intensely hot central star (SAO 20575).
Also designated Sharpless 162, and Caldwell 11, this unmistakable emission nebula sits within a giant, glowing molecular cloud. The Bubble itself is about 10 light-years in diameter.
The Bubble Nebula in Cassiopeia.
The image shown above was captured from my backyard using a refractor telescope, and a monochrome CCD camera. To learn more about astrophotography and how you can start taking photos of the night sky, be sure to visit the get started section of this website.
Bubble Nebula Details
- Common Name: The Bubble Nebula
- Type: Emission Nebula
- Cataloged: NGC 7635, Sharpless 162, Caldwell 11
- Constellation: Cassiopeia
- Distance: 7,100 light-years
- Magnitude: 10
- Apparent dimensions (V): 15′ × 8′
The Bubble Nebula lies very close to an impressive open star cluster known as Messier 52. This star cluster can be photographed within the same field of view as the Bubble Nebula using a wide-field telescope or telephoto lens.
This area of Cassiopeia is populated with several interested nebulae regions, including the Lobster Claw Nebula. With the right magnification, you can capture the Bubble Nebula and Lobster Claw Nebula within a single frame.
The Lobster Claw Nebula and Bubble Nebula in Cassiopeia.
Through a telescope with enough aperture under dark skies, the Bubble Nebula appears as an extremely faint shell around the central star. You will need dark skies to view the Bubble Nebula visually, it is not possible for me to observe this faint emission nebula from my city backyard.
Like many of the deep-sky objects you see not this website, I have only seen them appear in images with my camera, and never with my own eye through the telescope eyepiece.
Astrophotography
Through long-exposure photography, amateur astrophotographers can collect the light emitted by this nebula over long periods of time. My best image of the Bubble Nebula includes roughly 6-hours of total exposure time.
Narrowband filters are recommended when photographing the Bubble Nebula. Unlike broadband deep-sky targets such as galaxies or reflection nebulae, NGC 7635 does not reveal its best self in traditional RGB imaging.
Emission nebulae are especially pleasing to the eye with the help of an h-alpha filter. The image below shows what the Bubble Nebula looks like when photographed with an H-alpha filter (Astronomik 6nm 1.25″ filter) and a monochrome CCD camera.
The Bubble Nebula in Ha
The 6nm bandpass of the hydrogen-alpha filter allows a very narrow wavelength of light to pass through to the camera sensor in the 656nm range. This is helpful when isolating the light emitted from the Bubble Nebula from a light-polluted sky.
A monochrome CCD camera is an ideal choice for narrowband imaging, as it allows much more signal to reach the camera sensor than a traditional, daytime (color) camera. I typically use a Starlight Xpress 694 Monochrome CCD camera to take my narrowband images, but there is value in shooting narrowband filters for one-shot-color astronomy cameras as well.
There are several types of telescopes to choose from, but I prefer to use an apochromatic refractor for astrophotography (here are some of the ones I recommend). For my latest image of the Bubble Nebula, I used a large Sky-Watcher Esprit 150 refractor telescope with a focal length of 1050mm. You can see a picture of my imaging setup below.
My apochromatic refractor telescope (Sky-Watcher Esprit 150).
The Bubble Nebula resides in the northern constellation Cassiopeia. For amateur astrophotographers at mid-northern latitudes, the best time to photograph the Bubble Nebula is in the fall.
I typically begin shooting this emission nebula in August and continue to collect new exposures throughout September and October. I have photographed the Bubble Nebula many times, through several different camera and telescope configurations.
More Nebulae in Cassiopeia:
