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NGC 2818
Open Cluster and Planetary Nebula
aka NGC 2818, PNG 261.9+08.5, PK 261+08.1, He 2-23, ARO 508, ESO 372-13 (PN)
aka NGC 2818A, Melotte 96, Collinder 206, Raab 82, OCL  743 (OC)
RA: 09h16m01.5s Dec: -36°36'37" (PN) (Pyxis)
Integrated Visual Magnitude: 13.0 (PN) 9.9 (OC)
Angular Diameter: 50" (PN) 9' (OC)
Mean Surface Brightness: 21.2 Mag/arc-secē (PN)
Distance 6000-10000 ly
Age: 600 to 1000 Myrs (OC)

Minimum requirements to detect: 4-inch under dark skies


Where the heck have I been?  That's what I found myself thinking as I looked at this wonderful planetary nebula embedded in an open cluster.  These two objects both share an NGC number and some references use the designation 2818A to describe one or the other of the two.  Planetary nebulae in open clusters make for a rare visual treat and the planetary that appears to lie in M46 is one of my all-time favorite objects.  So how had I overlooked NGC 2818 all these years?  And why isn't it better known?  The only answer I can come up with is that NGC 2818 are pretty far south and lie in a little-observed constellation (at least for us northerners).  From the latitude of Los Angeles (33N) this pair only transits 20o of above the horizon. But provided you observe near maximum altitude this is high enough for a pretty good view.  In mid-February NGC 2818/A transit between 11 PM and midnight.

The planetary nebula NGC 2818 is relatively large and bright with interesting structure.  This planetary is similar in size and brightness to the much better known "Bug" (NGC 6302) in Scorpius.  It's relatively high surface brightness takes magnification well.  Look for the appearance of two separate parallel lobes that arc toward one another, nearly touching at the ends.  Also look for a fainter outer envelope, particularly off each end, using averted vision.  I didn't detect any color but Steve Coe notes that, "A few dark lanes are seen in the planetary at 165X, it is light green at all powers."  Although NGC 2818 has a lower surface brightness than NGC 2438 (the PN in M46) it does compare favorably and its intriguing structure will surely bring me back again and again.

The NGC 2818 cluster is fairly faint, mostly made up of 11th to 14th magnitude stars.  It is scattered and irregular and does not immediately jump out at you as a cluster of stars.  It doesn't begin to compare to M46.  Regardless, the many stars do make a nice backdrop for the planetary.  Interestingly, NGC 2818 is the only cluster-planetary combination that is currently believed to be truly associated.  Although the status of NGC 2438 as a member of M46 is not known for certain, most indications are that the planetary is a foreground object.  And the relatively young age of M46 makes the possibility of one of it's member stars being the progenitor of the planetary nebula fairly remote.  The NGC 2818 cluster, on the other hand, is older (perhaps as old as  Billion years).


The field in a 12-inch at 75x.  North is down and east is to the right.
Millennium Star Atlas Vol II Chart 923
Sky Atlas 2000 Chart 20
Uranometria 2000 Vol II Chart 364
Herald-Bobroff Astroatlas B-06 C-58