Planetary Nebula in M46

Messier 46 is a rich cluster of young stars with a beautiful ring shaped planetary nebula with three stars within the ring – giving it the appearance of a human face.

It is seemingly embedded within the M46 cluster. However, the planetary nebula (NGC 2438) is not a part of M46 because it is:

(a) travelling at a different speed to the cluster;
(b) an old dying star, whilst the stars in the cluster were “recently” born; and
(c) believed to be much closer than the cluster’s distance of about 5,400 light years.

Planetary nebulae are favourite objects of mine. Other recent images include Shapley-1 and the exquisite Helix Nebula.

Zoomed in  a bit.
Zoomed in a bit.

Object Details:

NGC 2438, PK 231+04.2, W43.
Constellation: Puppis
Location: in open cluster M46 (NGC 2437).
Visual magnitude: 11.5
Apparent size: 1.2′
Distance: 2,900 or 3,300 light years according to different reference sources.
Altitude: 41° above East horizon.


Exposure: 46.7 minutes. Live stacked.
Gain 300
Date: 2018-12-26 commencing approx 11.05 pm
Location: Leumeah, NSW.

Picture saved with settings embedded.
Zoomed in a bit more


Sky: outer suburban.
Cloud: no.
Moon: rose towards end of session.


Image acquisition software: SharpCap.
Image post-processing:  GIMP.
Cropping: no.

Geek Log

[ZWO ASI071MC Pro]
Output Format=PNG files (*.png)
Capture Area=4944×3284
Colour Space=RGB24
Hardware Binning=Off
Turbo USB=80(Auto)
Frame Rate Limit=Maximum
Timestamp Frames=Off
White Bal (B)=55(Auto)
White Bal (R)=29(Auto)
Cooler Power=0
Target Temperature=-15
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Anti Dew Heater=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1

Imaging telescope: Skywatcher Esprit 120ED Super APO triplet refractor.
Focal length: 840 mm, focal ratio: f/7.
Imaging camera: ZWO ASI 071 MC Pro
Guiding: no.
Telescope mount: SkyWatcher EQ6-R Pro.
Polar aligning method: QHYCCD PoleMaster.
Polar alignment error: <10′.
Field flattener: yes; filter: no.

Observing Notes:

Imaged with SharpCap Live Stack from 11.05pm to 12.12 am (67 min) obtaining 115 x 24.169 sec frames.

Recorded 2803 seconds of exposure (46.7 min), so 20 mins were ignored by Live Stack, before I increased the FWHM from about 4 to 6.1.

Moon rose behind the trees at 11.19 pm but I did not notice it until about 11.45 when it was still a subdued colour. By midnight it was getting brighter, so I terminated imaging at 12.12 am.


My planetary nebula portfolio

My gear.


See next post for details of additional planetary nebulae in Messier 46.

Image © R.Powell



  1. As I first came across this tonight, I missed the word “IN” and thought you were referring to M46 as a planetary nebula. Although it’s been well over 50 years since I last viewed this cluster, I still recall it as being in Puppis!
    The un-imaginably beautiful photographs you are capturing today display this pretty little planetary (which I also have checked off as “seen” in my old NGC Catalog.) (My historic notes of those personal observatopns is at another location, but you can be sure I’ll be looking is up when I get there later this week.) In addition to your usual supurb photos, thanks as well for the vivid informative descriptions. Marty 🙂

    Liked by 1 person

    1. Thanks, Marty. Yes, there is sometimes confusion when objects with separate identities lie in the same field. (The Rosette nebula might be considered a prime example).
      Personally, I have difficulty remembering Messier numbers, let alone NGC numbers and will usually refer to this particular object as “the planetary nebula in M46” for personal convenience.
      Thanks for your kind remarks and visits, both always appreciated.


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