Observing at Skyhound

observing.skyhound.com

 

Home   Deep Sky   Shallow Sky   Comet Chasing   Observing Handbook   Meet the Skyhound   Contact


Abell 31
Planetary Nebula
aka A 31, PN G219.1+31.2, PK 219+31.1, ARO 135
RA: 08h54m13.2s Dec: +08°535'3" (Cancer)
Integrated Visual Magnitude: 12.2
Angular Diameter: 16.8'
Mean Surface Brightness: 27.0 Mag/arc-secē
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 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 (right) 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 at 35x.  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