NGC 1501, Oyster Nebula

NGC 1501
NGC 1501: Planetary nebula in Camelopardalis; 500 mm Cassegrain 3625 mm f/7.2; SBIG STL11K; 20+10+10+10 min LRGB; Bernese Highlands; © 2011 Radek Chromik


This planetary nebula was discovered by William Herschel on November 3, 1787 using his reflecting telescope of 18.7 inch diameter and 20 feet focal length. He cataloged it as IV 53 and noted: «A pretty bright planetary nebula. Near 1' diameter, round, of uniform light and pretty well defined. 2 observations with 360 magnified; but still pretty abruptly defined, and a little elliptical.» [464] His son John cataloged it 1864 as GC 801 and Dreyer later in 1888 as NGC 1501. [313]

Physical Properties

NGC 1501
NGC 1501: Image taken with Hubble Space Telescope [224]

NGC 1501 is specified in the Vorontsov-Velyaminov classification scheme as an irregular disk (type III). The irregular texture is particularly striking on photographic and CCD images. If you were to compare the mist with something earthly, it looks most like an oyster! The central star of the nebula belongs to the class of Wolf-Rayet stars. These are stars with a very hot surface from which a particularly strong wind emanates. So they are characterized by an extremely high loss of mass. [26] The distance from NGC 1501 is given as about 4000 light years. The diameter of the gas envelope is about a light year. [158]

The central star is an irregularly variable with a tiny amplitude of 0.1 mag. Roger N. Clark gives in his excellent book «Visual Astronomy of the Deep-Sky» [26] the brightness of the central star as 13.5 mag. In the «Deep Sky Field Guide to Uranometria» [22], however, there is a value of 14.45 mag.

— 1996, Philipp Reza Heck

«Strasbourg-ESO Catalogue of Galactic Planetary Nebulae» Acker et al., 1992 [141]
DesignationsPN G144.5+06.5: NGC 1501, PK 144+06.1, ARO 44, VV 16, VV' 22
Right Ascension (J2000.0)4h 07m 01s a
Declination (J2000.0)60° 55' 03" a
Dimensions 52." (optical)
Distance 2.0 kpc :
Radial Velocity+36.2 km/s ± 1.4 km/s
Expansion Velocity 37.0 km/s (O-III)
C-Star DesignationsAG82 26, CSI +60 -04027, GCRV 2334, PLX 894
C-Star Magnitude14.34 mag (U filter), 15.17 mag (B filter), 14.39 mag (V filter)
C-Star Spectral TypeWC 6-7,OVI, WC early
DiscovererHERSCHEL 1787

Finder Chart

The planetary nebula NGC 1501 is located in the inconspicuous constellation Camelopardalis, which is located between the more well-known constellations Cassiopeia and Auriga. The telescope is aligned using the Telrad finder as shown on the map below. The PN is roughly in the middle between the stars. β Camelopardalis (4.0 mag) and CS Camelopardalis (4.3 mag).

Chart NGC 1501
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

NGC 1501
NGC 1501: Zeichnung; 200mm SCT, 226x; © 1996 Philipp Reza Heck

200 mm aperture:As with almost all PN, a high magnification (over 200x) is necessary here in order to be able to find fine details. The first thing you notice is the slightly elliptical shape of the nebula. In the 200 mm telescope (f/10) and with good dark adaptation, one can clearly see that the inner area of the pane has an irregular distribution of brightness. Weaker areas south-east of the center are particularly prominent.

The central star is clearly visible in the 8-inch model with indirect vision. Apart from good seeing, you have to be lucky that the star is at its maximum brightness. The slight fluctuation in brightness of the central star would normally not be perceptible to the naked eye. However, since the brightness of the star in the 8-inch model is at the visual limit of perception, this small amplitude is still important.

— 1996, Philipp Reza Heck


22«The Deep Sky Field Guide to Uranometria 2000.0» by Murray Cragin, James Lucik and Barry Rappaport; Willmann-Bell, Inc.; ISBN 0-943396-38-7
26«Visual Astronomy of the Deep Sky» by Roger N. Clark; Cambridge University Press
141Strasbourg-ESO Catalogue of Galactic Planetary Nebulae; A. Acker, F. Ochsenbein, B. Stenholm, R. Tylenda, J. Marcout, C. Schohn; European Southern Observatory; ISBN 3-923524-41-2 (1992); (2021-02-18)
149SkySafari 6 Pro, Simulation Curriculum;
158NOAO Image Gallery;
160The STScI Digitized Sky Survey;
224Hubble views a cosmic oyster and pearl in NGC 1501; (2021-01-10)
313«A New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel, Bart., revised, corrected, and enlarged» Dreyer, J. L. E. (1888); Memoirs of the Royal Astronomical Society. 49: 1–237; Bibcode:1888MmRAS..49....1D
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