Abell 12
Planetary Nebula
aka PNG 198.6-06.3, PK 198-06.1, Abell 12, ARO 220
RA: 06h02m21.4s Dec: +09°39'07" (Orion)
Integrated Visual Magnitude: 13.9
Angular Diameter: 37"
Mean Surface Brightness: 21.5 Mag/arc-sec²
Distance 6900 ly

Minimum requirements to detect: 8-inch and OIII filter under suburban skies

Abell 12 is an interesting planetary nebula that is a challenge to observe due to its proximity to the 4th magnitude star Mu Ori.   Mu ori is the next star up the chain to the north from Betelgeuse, so finding the field is quite easy.  Making out the nebula in the glare of the star is something altogether different.  The trick to finding Abell 12 is to use an OIII filter.  The UHC filter helps some, but it takes the OIII to really bring it out.  I had tried several times and failed to see this planetary in my 18-inch without a filter.  When I finally inserted an OIII it popped right into view!
To me Abell 12 looked like a blob within the bright halo of Mu Ori.  The nebula appeared to almost touch the star.  I thought I detected a ring, or donut shape.  The image above confirms the ring and is quite intriguing.  The bright object with the blue halo is Mu Ori.  The smaller object to the left (east) is the planetary.  The edge of the nebula forms a bright, thin, regular ring, that doesn't quite close onto itself.  Quite odd!  Dave Aucoin wrote that he "observed elongated structure much like a lenticular in shape" in a 13.1" Dob. 


The field in an 6-inch f/8 at 50x.  North is down and east is to the right.
Millennium Star Atlas Vol I Chart 204
Sky Atlas 2000 Chart 11
Uranometria 2000 Vol I Chart 181
Herald-Bobroff Astroatlas B-05 C-40

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