| The
open cluster M46 is famous for the fine planetary nebula that lies
superimposed upon it. But did you know that another planetary
lies a mere 30' north of the cluster center? Minkowski 1-18 is
small and faint, and few people know about it. Without an OIII
filter it is out of reach of even an 18-inch telescope under dark
skies. But the OIII (and UHC) have brought this planetary
within reach of larger amateur instruments. It's not clear
what the minimum aperture is required to see it, but based on my
observations I'd say that it should be detectable in a 14-inch
scope, if not a 12 inch. It should be a real treat for those
with access to 20-inch or larger scopes.
Here is my log entry
from January 2001 with my 18-inch f/4.5:
With the OIII in place M
1-18 became readily apparent at 166x and just bright enough to
sustain 430x with averted vision. It appeared round and very
diffuse; no obvious structure was seen. I had the impression
at times of a fairly sharp, slightly ragged, edge. With the
OIII removed I saw nothing.
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