M 46 (NGC 2437) and NGC 2438 (PK 231+4.2) Open Cluster and Planetary Nebula in Puppis

M 46 is Located at: RA 07 hours 41 minutes 47 seconds, Dec -14 degrees 48 minutes 36 seconds

Size: 27' (20') Magnitude: 6.1 Class: II 2 r

Note: The Planetary Nebula NGC 2438 is located in the north/central part of the cluster, and is not associated with it:

Size: 64" Magnitude: 10.1 photographic Class: 4+2

North is up

West to the right


 8" f5 Newtonian reflector


  ST-8XME, self-guided, binned 1x1, temp -25c, camera control MaxIm DL 4.56


Lumicon Red filter, 540 minutes  (54 x 10 minute subs) 03/11/12/14/2010; seeing 2.2-4.7 FWHM per CCDStack


CCDStack 1.6.1, Photoshop 7.0


 Rolling Roof Observatory, Thousand Oaks, CA 91360 (+34d 13m 29s -118h 52m 20s)


This is a re-shoot of one of my last Track & Accumulate images from 2006. Seeing was much better than during the recent M 47 image, but I did not get all the data I wanted because of weather... Finished up on the 14th, however, during the last few images the seeing deteriorated quite a bit.

According to "Star Clusters", by Brent Archinal and Steven Hynes, the size of open cluster M 46 is 20 arc minutes.

From the NGC / IC Project:

Contemporary Visual Observation(s) for NGC 2437
NGC 2437 = M46 = Cr 159
07 41 47 -14 48.6
V = 6.1;  Size 27

17.5": At 100x M46 fills a large portion of the field and there are a few 
hundred stars fairly evenly distributed in a 35' field.  The cluster appears 
slightly elongated E-W although there are no clear borders. There is no increase 
in concentration towards the center and except for two brighter stars on the W 
side the cluster is unusually uniform in brightness (mag 11-13) and distribution 
in the main body.  There is a noticeable 2' void, though, very close to the 
center of the cluster.  Around the periphery the distribution becomes quite 
scraggly and the cluster mixes with the general field density.  The beautiful 
annular planetary N2438 is situated in the north side of the cluster.

8": bright, very rich, large, includes a couple of mag 9 stars but most stars 
are mag 10-13 and fairly uniform in magnitude and distribution except for a gap 
near the center.  Contains the striking pn N2438 at the NE edge.

- by Steve Gottlieb
Contemporary Visual Observation(s) for NGC 2438
NGC 2438 = PK 231+4.2 = PN G231.8+04.1
07 41 50.6 -14 44 07
V = 11.5;  Size 73"x68"

17.5" (3/2/02): at 280x this is a beautiful, 1' diameter PN with a darker 
central hole at 280x situated on the NE side of the rich oc M46.  A mag 13 star 
(not the central star) is within the central hole slightly offset NW of center.  
The rim is fairly uniform but slightly brighter along the NE side.  The 20" 
central hole is clearly darker although there is not a dramatic contrast.  A 
brighter mag 11 star is just off the SE edge (about 15"-20" SW of the mag 11 
star a faint mag 14-15 star was also intermittently visible) and a string of 
faint stars oriented WNW-ESE is just over 1' S.  M 1-18 is located 22' NNE of 

13": annular planetary on the NE side of M46!  Fairly bright, moderately large, 
round, 1.0' diameter.  A mag 11 star is just off the SE edge and a mag 13 star 
is just NW of the geometric center (this is not the central star).  A third 
extremely faint star lies on the SW side.

8": slightly darker center, fairly small, round.

- by Steve Gottlieb