I can't say I enjoyed this observation, in fact it was a night of frustration and disappointment, but the joy came in the last 5 minutes of the night when I finally bagged my prize.
I went to bed early because there seemed no chance for astronomy: the moon was up, and icy winds were building which, as predicted, led to snow later. I was reading about a planetary nebula, Abell 12, which sits almost on top of the naked eye star Mu Orionis. I looked out the window and could see the star!
This was obviously the Universe calling, so I headed the call. 10 minutes later I was dressed and at the eyepiece and searching for the PN (another joy: having the scope observation-ready in a shed: just wheel it out and off you go) . At 40 arcseconds across and 12.4 mag, I thought I'd be able to spot it, even with the Moon up, as it was on the opposite side of the sky, but it was a complete fail. I gave up after about 40 minutes of trying every magnification, eyepiece and filter.Nothing.
Since I'd come this far, I thought I'd try Jonckheere 320 (also known as J320 or PN G190. 3− 17.7) also in Orion. It's a planetary nebula with an unusual and complex structure, a "poly‐polar planetary nebula surrounded by point‐symmetric knots". I'd read about it earlier in the day but hadn't planned to observe it any time soon, and had no idea what it looked like.
Harrington's book Cosmic Challenge lists it as 12.9 magnitude and a tough one for scope of 6" -9.25" aperture, but it's possible, he says, with an 8" scope even with suburban light pollution. The problem is its size: 26 X 14 arc seconds. It was actually mis-catalogued as a double star by Robert Jonckeere until he revisited it in 1916 using the 28 inch refractor at the Royal Greenwich Observatory.
Long story short: I couldn't find it. With the light pollution and moon, I got mixed up as to which star to begin the star hop in Orion's bow. But I kept at it for an hour, and eventually honed in on the star field. At that exact moment thick cloud rolled in. I waited inside for 15 minutes and it cleared a bit, I rushed out and clouds rolled in again.
With almost 3 hours and nothing to show for it, I was wondering why I'd bothered, then there was a break in the clouds and I got it! I managed the briefest of observation, and just managed a sketch before it was gone.
Here's the result. The OIII filter didn't seem to help much and the only way to glimpse any structure was at 546X. Yet it still was very tough to pick out anything even at that magnification. It appeared as a disc to begin with, then there were hints of elongation, giving it an ovoid shape. Just for a few seconds I saw what looked like a brighter knot at one end.
Under the sketch is a comparison with the Hubble image. I was pleasantly surprised to see the reasonable match, as my observation of the shape and the brighter knot was very tentative and fleeting, and the sketch was rushed in a minute or two. I'm pleased I hadn't looked at any images of it before observing and finishing the sketch, otherwise it would have been very easy to confuse what I was seeing with what I was expecting to see.
Edited by iainp, 22 November 2015 - 12:42 PM.