| Planetary
Nebula
aka PNG 219.1+31.2, PK 219+31.1, ARO 135 RA: 08h54m11.4s Dec: +08°54'30" (Cancer) Integrated Visual Magnitude: 12.2 Angular Diameter: 16.2' Mean Surface Brightness: 26.9 Mag/arc-sec² Distance 1000 ly Minimum requirements to detect: 8-inch under dark skies |
Abell
31 is a large, faint planetary nebula that is best viewed at low magnification.
An OIII filter is required to see it in all but the largest scopes.
Many observers report seeing a large, round glow. Look for a prominent
parallelogram of four 10th magnitude stars. The brightest portion
of the nebula envelopes the south-eastern star, extending toward the star
to the southwest.
In my 18-inch f/4.5 at 94x, I at first only had a very vague impression that anything was there, even with the OIII in place. Scanning the field helped, as the glow often jumped out at me as it came into view, only to become vague yet again. The overall impression was of an egg-shaped glow elongated in the east-west direction. In time, I began to suspect two "streaks" that formed a narrow, elongated horseshoe shape. This horseshoe looped around the south-eastern star. The H-Beta filter also brought out the nebula, although not quite as well as the OIII, and the "horseshoe" wasn't nearly as obvious. I did suspect the vaguest impression of a glow without a filter, but I could not be certain.
The morphology of this planetary nebula is very interesting. It is apparently an ancient planetary that is interacting with the surrounding interstellar medium. Note how the color DSS image above shows both red and blue portions to this nebula. The blue portion sits close to the progenitor star and shines strongly in OIII. The southern (top) portion is bounded by a wide "bow shock" where the nebular material is apparently interacting with the surrounding medium.
The field in an 8-inch f/5 at 50x. North is down and east is to the right.
| Millennium
Star Atlas Vol II Chart 760
Sky Atlas 2000 Chart 12 Uranometria 2000 Vol I Chart 187 Herald-Bobroff Astroatlas B-05 C-40 |
