Bubble Nebula (NGC 7635) + Messier 52

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

Bubble Nebula (NGC 7635)

NGC 7635 was discovered by Wilhelm Herschel on November 3, 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]

NGC 7635
NGC 7635: Buble Nebula in Cassiopeia; 500/2500mm-Newton + SBIG ST-6; Observatory Bülach; © 1996 Stefan Meister

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]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 7635
Right Ascension23h 20m 45.0s
Declination+61° 12' 42"
Diameter15.00 × 8.0 arcmin
Photographic (blue) magnitude11.0 mag
Dreyer DescriptionvF, * 8 inv l excentric
IdentificationLBN 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 September 7, 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] [4]

NGC 7635
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 Mihajlovic
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
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
«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 7654
TypeOCL (I2r)
Right Ascension23h 24m 48.0s
Declination+61° 36' 00"
Diameter16.00 arcmin
Visual magnitude6.9 mag
Dreyer DescriptionCl, L, Ri, mCM, R, st 9…13
IdentificationM 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.

Chart NGC 7635
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [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


4«Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System» by Robert Burnham; Dover Publications, Inc.; Voume I: ISBN 0-486-23567-X; Volume II: ISBN 0-486-23568-8; Volume III: ISBN 0-486-23673-0
125Aktuelle Hinweise für den Beobachter; SuW 8-9/94, S.635
145SIMBAD astronomical database; simbad.u-strasbg.fr/simbad
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)
464«Catalogue of a second thousand of new nebulae and clusters of stars; with a few introductory remarks on the construction of the heavens» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1789; DOI:10.1098/rstl.1789.0021