Bubble Nebula

For the Bubble Nebula in Barnard's Galaxy, see Bubble Nebula (NGC 6822).

NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region^[1] emission nebula in the constellation Cassiopeia. It lies close to the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7^[1] magnitude young central star, SAO 20575 (BD+60°2522).^[7] The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow.^[7] It was discovered in November 1787 by William Herschel.^[5] The star BD+60°2522 is thought to have a mass of about 44 M_☉.

Bubble Nebula

Emission nebula
H II region
Wide field image of NGC 7635 as captured by the Hubble Space Telescope
Observation data: J2000 epoch
Right ascension	23h 20m 48.3s[1]
Declination	+61° 12′ 06″[1]
Distance	7100[2] to 11000[3][4] ly   (3,400 pc)
Apparent magnitude (V)	~10[5]
Apparent dimensions (V)	15′ × 8′[6]
Constellation	Cassiopeia
Physical characteristics
Radius	3[2] to 5[7][4] ly
Notable features	Shell around SAO 20575[1]
Designations	Bubble Nebula[1] Sharpless 162 (Sh2-162) Caldwell 11
See also: Lists of nebulae

Amateur observation

NGC 7635 and its environs imaged through an 8-inch amateur telescope

With an 8-or-10-inch (200 or 250 mm) telescope, the nebula is visible as an extremely faint and large shell around the star.^[6][1] The nearby 7th magnitude star on the west hinders observation, but one can view the nebula using averted vision.^[6] Using a 16-to-18-inch (410 to 460 mm) scope, one can see that the faint nebula is irregular, being elongated in the north south direction.^[6]

See also

• Lists of nebulae