NGC 1501 in Camelopardalis
November 2025 - Nebula and Cluster of the Month
Nestled in the southern reaches of the faint stars that make up the busy but often overlooked polar constellation of Camelopardalis (the giraffe - so named because it was once thought that a giraffe was the result of an unlikely cross between a camel and a leopard), lies the planetary nebula NGC 1501.
As should be expected, this was a discovery of William Herschel, who first saw it on the night of 3rd November 1787. He placed the object in his fourth category – planetary nebulae – as 53 H.IV, adding the description A pretty bright planetary nebula near 1' diameter. Round. Of uniform light and pretty well defined. Two observations [were made] with 360[x] magnified in proportion; but still pretty abruptly defined, and a little elliptical.
The planetary nebula lies in a region of the sky surprisingly devoid of bright stars, especially considering that the Milky Way runs right through it. The closest star of any brightness is the 4th-magnitude β Camelopardalis, and that’s 7° away.
NGC 1501 has a very complex morphology. Although to the visual observer it appears as a fairly smooth and round or oval, this belies the true complexity, which can be seen in the Hubble image below. Spectroscopic and imaging studies made by Sabbadin et al in 2000 reveal that NGC 1501 is not a smooth, spherical shell but possesses numerous protrusions and lobes on an overall ellipsoidal body. The authors described it as a ‘boiling, tetra-lobed shell’.1
The central star bears the variable star designation CH Camelopardalis and has a spectral type of [WC4], a hydrogen-deficient, carbon-rich, Wolf-Rayet star with a surface temperature of around 100,000K. It displays multiple periodicities between 19 minutes and 87 minutes, the strongest of which are found at 31, 45, 56 and 87 minutes. Magnitude variations are typically small, ranging from 0.02 to 0.05 magnitude, but there are rapid, irregular fluctuations caused by the resonance of several close modes.2
The star has a mass of about 0.55 solar masses, a very high stellar wind, and is on the cusp of the final phase of its life; white dwarf cooling.3
To the visual observer, all of this can only be of academic interest. The nebula is fairly bright – magnitude 11.5 in most listings, but sometimes quoted (incorrectly, I think) as 13.0. It measures about 60” by 55”, but usually looks pretty round.
The central star is magnitude 14.5. Some observers say they can see it clearly with telescopes as small as 8” aperture. Others say otherwise. The observation I present here was made with my 12” Newtonian under sub-optimal conditions, and I didn’t see it, though there is a small, brighter patch in the centre.
When I made the observation, I wrote in my journal Quite large and immediately visible to direct vision even without the OIII filter. Round. With the OIII filter it appears occasionally to be darker in the middle, possibly with two voids. Very slightly elongated.
In The Night Sky Observer’s Guide, the object is described as seen through a 12” – 14” telescope as showing the same darkening as I saw. ... The centre is slightly darker, its annularity being more noticeable at higher power.
The author goes on to say that the central star was prominent.
As usual with planetary nebulae, it is worth using an OIII filter. This often brings out more detail and structure than can be seen without. Central stars should be searched for, however, without an OIII or Nebular filter, as these tend to suppress continuum emission.
NGC 1501, then, is far more than a simple glowing shell. It is a dynamic, turbulent and chemically diverse structure surrounding a complex, pulsating hydrogen-deficient star. Its study sheds light on the final stages of stellar evolution and the physical processes shaping planetary nebulae, confirming Herschel’s eighteenth-century discovery as one of enduring astronomical importance.
| Object | RA | Dec | Type | Magnitude |
|---|---|---|---|---|
| NGC 1501 | 04h 07m 0s | +60° 55’ | Planetary nebula | 11.5 |
References:
- Sabbadin, F., Benetti, S., Cappellaro, E., Ragazzoni, R., Turatto, M. & Costa, E., 2000. The True Shape and Structure of Planetary Nebulae: NGC 1501. Astronomy & Astrophysics, 355, pp.688–696.
- Bond, H. E., Ciardullo, R. & Meakes, M. G., 1996. Pulsations of the Hydrogen-Deficient Central Star of the Planetary Nebula NGC 1501. Astronomical Journal, 112(6), pp.2699–2707.
- Ercolano, B., Wesson, R., Zhang, Y., Barlow, M. J., De Marco, O., Rauch, T. & Liu, X.-W., 2004. The 3D Photoionisation Structure of the Planetary Nebula NGC 1501 and its Hydrogen-Deficient Central Star. Monthly Notices of the Royal Astronomical Society, 354(2), pp.558–576.
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Cluster of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
