NGC 7635, also known as Caldwell 11 and the Bubble Nebula, is a beautiful emission nebula located in the constellation Cassiopeia, which is best viewed in autumn.
Suburban dwellers with a moderate-sized scope (8+ inches in diameter) may be able to spot this emission nebula. The nebula will appear as a very faint smudge, or a wisp of haze, in the eyepiece. I feel using averted vision is a must to make it out.
A “brighter” 8.7 magnitude star lies inside the bubble of gas and dust. It’s this star that’s creating the alluring orb we see today. According to NASA, stellar winds rushing four million miles per hour carry “particles from the star’s surface and help propel the ‘shock wave’ outward. The result ends up looking something like a planetary nebula, in which a star’s outer layers expand outward, but it is in fact gas and dust from the surrounding nebula that’s being pushed away from the star.” 1 The hot, mind-numbingly fast stellar wind continues to blow out the surrounding molecular cloud. The nebula itself measures around six light years in diameter.
This activity all happens quietly for us as we sit on the sidelines some 7,000 light years away.
Credit goes to astronomer William Herschel who first recorded the nebula in November 1787, almost 236 years from when I first observed the object from my backyard.
My Observations
| Date | November 18, 2022 |
| Time | 8:20 p.m. |
| Location | Seattle, WA |
| Magnification | 169x |
| Scope | Meade 8″ SCT |
| Eyepiece | 12mm |
| Seeing | Good |
| Transparency | Good |
Searching for this nebula reminds me of finding NGC 40—both are so faint, especially from my suburban location! I almost left both these objects behind, but I’m glad I kept looking for their faint, diffuse light to sneak into the eyepiece. I had to slightly nudge the scope left and right, while using averted vision, to see Caldwell 11 hiding in the suburban skies. Of note, I see two stars near, or in, the nebula oval area. I’m fairly certain one is the +8.7 mag star that’s creating the bubble, but I’m unsure of the other. I’ll need to research other sketches.
It’s a shame this Bubble Nebula is so faint. Photos of it are astounding and gorgeous.
Key Stats
| Constellation | Cassiopeia |
| Best Viewing | Autumn |
| Visual Magnitude | +11 |
| Absolute Magnitude | +2.83 |
| Distance from Earth | 7,000 ly |
| Diameter | 6 ly |
| Apparent Size | 15 x 8 arcmin |
| Milky Way Location | Orion Spur |
| My Viewing Grade | D |
| Designations | C 11, NGC 7635, Sharpless 162 (Sh2-162), LBN 548 |
Sources and Notes
Banner photo credited to NASA, ESA, Hubble Heritage Team. This file is in the public domain because it was created by NASA and ESA. Source details here.
1 Henderson, Edward. “Caldwell 11.” NASA, NASA, 1 Oct. 2019, https://www.nasa.gov/feature/goddard/caldwell-11.
Sketch by Wayne McGraw
The Garden Astronomer 