Bubble Nebula (NGC 7635) + Messier 52

NGC 7635
NGC 7635: Bubble Nebula in Cassiopeia; Takahashi TSA-120 f=900 mm; Canon EOS 20Da; 9 x 8 min, ISO 800; Gurnigel; © 27. 8. 2011 Jonas Schenker [34]
NGC 7635
NGC 7635: Buble Nebula in Cassiopeia; 500 mm Cassegrain 5800 mm f/11.4; SBIG STL11K; 15+15+10+15 min LRGB; Bernese Highlands; © 2005 Radek Chromik [32]

Bubble Nebula (NGC 7635)

NGC 7635 was discovered by William Herschel on 3 November 1787. He cataloged it as IV 52. He described it as «a star 9 magnitude with very faint nebulosity of small extentent about it». [464] The distance is given as 2.41 kpc (7860 light years). [145]

It is a galactic H-II region. Within, believed to be near the edge of the nebula, stands a Wolf-Rayet star (SAO 20575), whose intense stellar wind has created a spherical bubble, giving this nebula its name. Other sources speak of an O star instead of a Wolf-Rayet star. O stars have less strong stellar winds than WR stars. NGC 7635 is sometimes classified as an uncommon planetary nebula, but has no PK number. [4, 125]

NGC 7635
NGC 7635: Buble Nebula in Cassiopeia; 500/2500mm-Newton + SBIG ST-6; Observatory Bülach; © 1996 Stefan Meister
Revised+Historic NGC/IC Version 22/9, © 2022 Dr. Wolfgang Steinicke [277]
Designation NGC 7635
Type EN
Right Ascension (J2000.0) 23h 20m 45.0s
Declination (J2000.0) +61° 12' 42"
Diameter 15 × 8 arcmin
Photographic (blue) magnitude 11.0 mag
Metric Distance 3.400 kpc
Identification, Remarks WH IV 52; h 2235; GC 4947; LBN 549; in Sh2-162, Bubble nebula

Open Cluster Messier 52

This is a beautiful star cluster of the open or galactic type, located in a Milky Way region on the western edge of the constellation near Cepheus. Charles Messier stumbled upon this star cluster while observing this year's comet on 7 September 1774. He described M 52 as a cluster of very small stars shrouded in a faint nebula. But on this point Messier was wrong. There is no nebula at or near M 52. The closest, at about half a degree, is NGC 7635.

M 52 belongs to the richer and more condensed open star clusters. Its calculated density ranges from over 3 stars per cubic parsec to 50 stars per cubic parsec near the center. The star cluster is one of the younger ones, comparable in age and type to the Pleiades. The main components are blue giants of spectral type B7. The two apparently brightest stars in this group are yellow giants of type F9 (7.77 mag) and G8 (8.22 mag). [4]

M 52 + NGC 7635
M 52 + NGC 7635: Overview shot. Cluster M 52, nebula NGC 7635, nebula NGC 7538, cluster NGC 7510; TS Triplet APO 90, Reducer Photoline 0.79 (490mm / f5.44), SBIG ST-8300; 15L x 300sec 1×1, 10R, 10G, 14B 2×2 300sec; Bernese Highlands; © 2018 Bernhard Blank, Dragan Vogel [32]
NGC 7635, M 52
NGC 7635, M 52: Bubble Nebula NGC 7635 with open cluster M 52; Celestron RASA 11" f/2.22; ZWO ASI6200 Pro; Tentlingen; © 2020 Peter Kocher [33]
NGC 7635, M 52
NGC 7635, M 52: Bubble Nebula NGC 7635 with open cluster M 52; Cassegrain 400mm f/3 + SBIG STL11000M; H-alpha:120min R:40min G:40min B:30min; Observatory Oberes Schlierental, Obwalden; © 2018 Eduard von Bergen [30]
Revised+Historic NGC/IC Version 22/9, © 2022 Dr. Wolfgang Steinicke [277]
Designation NGC 7654
Type OCL (I2r)
Right Ascension (J2000.0) 23h 24m 48.0s
Declination (J2000.0) +61° 36' 00"
Diameter 16 arcmin
Visual magnitude 6.9 mag
Metric Distance 1.421 kpc
Identification, Remarks h 2238; GC 4957; M 52; OCL 260

Where is Cassiopeia's Bubble?

The Bubble Nebula NGC 7635 and Messier 52 are located in the constellation Cassiopeia, which is circumpolar, but is highest in the sky at night in the months of July to January and is therefore best observed. If you take the distance from α to β Cassiopeiae and extend it beyond beta by a factor of 1.2, you come across the open star cluster M 52. There is another simple trick with the Telrad finder: M 52 has von Caph (β Cassiopeiae ) and from ι Cephei about the same distance. The telescope is aligned in such a way that the outermost circle of the Telrad lies on the line connecting the two stars and the center of the three concentric circles is at the same distance from the two stars. From M 52 we continue with an eyepiece with a large true field of view. About half a degree southwest of M52 lies nebula NGC 7635.

Finder Chart Bubble Nebula (NGC 7635) + Messier 52
Bubble Nebula (NGC 7635) + Messier 52 in constellation Cassiopeia. Charts created using SkySafari 6 Pro and STScI Digitized Sky Survey. Limiting magnitudes: Constellation chart ~6.5 mag, DSS2 close-ups ~20 mag. [149, 160]

Visual Observation

NGC 7635
NGC 7635: Drawing; 300mm f/4, 80x, O-III; © 9. 8. 1996 Bernd Nies

300 mm aperture: On a moderately dark night, when Cassiopeia is not particularly high in the sky, just the brightest part of the Bubble Nebula can be seen. A bubble shape is not yet visible. Without an O-III filter it is even invisible. An H-beta filter brings no improvement. On a very dark night with Cassiopeia near the zenith, NGC 7635 should certainly be visible more. The stars in the image below are from a printout. The number and position of the stars has not yet been corrected, only the 8.2 mag bright non-stellar object in the bright nebula has been added as a star. — 1996, Bernd Nies

762 mm aperture: Bubble Nebula NGC 7635 appears «on the right» as a crescent moon extending to a faint star, with the left part of the crescent being much bolder than the right, tapering one. — 30" f/3.3 Slipstream Dobsonian, Hasliberg Reuti, 3. 3. 2022, Eduard von Bergen

Objects Within a Radius of 15°