2013us10 20151221 arobertson

My sketch of the comet from this morning attached. I've had to go over the tails with my blender a bit more than I originally sketched it so they would scan. I had a look quite early on - about 4-ish but it was so low I couldn't see any hint of the tails. I commenced observing it in earnest about 5am when it was high enough to show the tails. I scrutinized it for about half an hour before I commenced sketching. I was using my 18" Dobsonian from my home address in Norfolk. Skies were about mag 5.5 with an SQM reading of 21.15 overhead. I examined it with a 21mm Ethos giving x98 and a full one degree FOV. A 20mm Pentax eyepiece with and without a comet filter and a 13mm Ethos with and without a comet filter.

 

It had a large brightish nucleus with a stellar core, as per my sketch there was a faint tenuous tail extending vertically towards the edge of the FOV, hard to define the exact cut off but it was around the edge of the field in the 21mm Ethos with the nucleus in the centre. I forgot to take a north position for position angle but with respect to this vertical tail there was a thinner longer one at the 8 o'clock position which extended right out of the FOV as far again - see sketch. Both very tenuous, the vertical one looked a bit wider. The comet filter didn't make much difference on the 8 o'clock one but the vertical one virtually disappeared so I can infer the vertical one was the dust tail and the '8' the Ion tail, so the comet filter had some use. Sketch was mainly done with the 21mm Ethos but I used the 13mm to tease out a bit more detail around the nucleus. At one point I started thinking, 'is there a short stubby tail in-between the two?' But scrutiny with the 13mm made me realise it was an extended part of the coma around the nucleus which wasn't in  the centre but offset somewhat. I finished observing it shortly after 6am - very enjoyable.