Caldwell 11 — Emission Nebula in Cassiopeia
NGC 7635
About Bubble Nebula
Description
The Bubble Nebula (NGC 7635) is an emission nebula in Cassiopeia, about 7,100 light-years away. The bubble is created by the stellar wind from the massive O-type star SAO 20575 (BD+60 2522), which blows a shell of gas about 10 light-years across.
Observing Tips
The bubble itself is very faint visually; at least an 8-inch telescope with an OIII or UHC filter is needed to see more than the bright star. Larger apertures (12-inch+) begin to reveal the arc of the bubble. Best in autumn evenings.
History
Discovered by William Herschel in 1787. The Bubble Nebula gained fame through Hubble Space Telescope imagery that revealed its nearly perfect spherical shell in stunning detail.
Fun Facts
The bubble is being inflated by a star 10-20 times more massive than the Sun with a surface temperature of 37,500 K. The bubble is not perfectly centered on the star because the surrounding interstellar medium is denser on one side.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Hard | V. hard+ | V. hard |
| 150 mm Newton 150mm Newt. | Medium | Hard+ | Hard+ |
| Celestron C8 (203 mm SCT) C8 203mm | Medium+ | Medium | Hard+ |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
With O-III filter
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Medium | Hard+ | Hard |
| 150 mm Newton 150mm Newt. | Easy | Medium+ | Medium |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Medium+ |
3Visibility
Set a location in User Settings to see visibility data.
4
Filter Response Guide
5
Eyepiece View
Bubble Nebula · 15.0′×8.0′ · N up, E left
Explore
6
Surface Brightness
Discover
7
Light Travel Time Machine
8
Relativistic Travel
Community Photos (1)
Credit: NASA, ESA, Hubble Heritage Team. License: Public domain. (Wikimedia Commons)
Skybred Mar 2, 2026
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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