I have hundreds of planetary nebulae tagged in my tablet's DSO Planner but they all appear under their PK designation. This means you can be looking at a well-known PN but not know it, which happened last week with PK 064+05.1 in Cygnus. It was listed as 10.4 magnitude and at a diameter of 10". Later I see estimates which place it as bright as 9 mag and 10" refers to the size of the faint outer shell; the main nebula is more like 5" or 6".
I was sure I had it somewhere in the 1 degree FOV at 100X but couldn't see anything where I thought it was apart from a red star. Looking at the edge of the FOV the star swelled in size! I realised this was the PN. Moving to 200X, the same effect was repeated: looking directly at the bright star made the nebula disappear. Only at 300X and better still at 600X could the nebula be viewed directly. But it was still red, so how could it be the planetary nebula??
I recorded it as a "blinking planetary" and wrote "red?" even though it clearly was red, I just couldn't accept the evidence of my eyes. To complicate things further, the longer I looked at high magnification the bluer it became. So I recorded it as blue too. I realised later this was due to my eyes adapting to the low light at high power and becoming less sensitive in the red part of the spectrum. When I looked again after drawing the view it was red again.
I had, of course, "discovered"... Campbell’s Hydrogen Star. The red and orange hues are caused by a glowing mix of hydrogen and nitrogen gases. I read later that a Hydrogen B filter can reveal the structure of its ring shape, but an observation the following day failed to show anything with the filter even at 900X, so that's a challenge for another day.
Here's the view at 300X and 600X in the box, with original notes below. The colour is what I saw at its most intense, which was at 300X. West is towards the lower left corner.
Edited by iainp, 18 May 2018 - 05:04 AM.