NGC 246 is a reasonably bright, 8th magnitude
planetary nebula that was discovered by William Herschel. Fairly
large as planetaries go, NGC 246 is of relatively low surface
brightness. It usually appears as a faint, round glow. McNeil
classifies this nebula as having an "irregular disk with traces
of ring structure."
The central star is HIP 3678, which is
responsible for creating the nebula as it puffs it's outer layers
out into space. It has a 14th magnitude companion 3.8" distant
at PA 129o.
The distance to this star system is 2100 light years, as measured by
HIPPARCOS. This distance implies an actual size of 6 light years for
the surrounding nebulosity. That's one and a half times the distance
from our sun to the nearest star. There are two other 11th magnitude
stars that lie within its glow. These are probably foreground or
background stars not associated with the nebula.
The view in a 6" at 50x. North is down and
east is right.
Although visible in telescopes
as small as 4 inches to a trained observer under dark skies, most
observers will require at least 6" to see it's faint, diffuse
glow. Don't use too much magnification as this planetary is
relatively large. Start by looking for a conspicuous group of four
11th magnitude stars. Once the field has been located, use averted
vision to look for a slight haze. Small scopes may only reveal the
brighter western half of the nebula. The central portion typically
appears much fainter than the image below shows.
I logged NGC 246 with my 18" f/4.5 Dob
without a filter:
"166x -- Very cool! Like a large bubble.
Two bright stars inside, one centered. One bright star appears at
the edge. The edges of the nebula appear brighter than the inside,
particularly near the star. Not much sign of structure except for
a rather strange appearance -- more of an impression -- that I can
only describe as eerie."