Comet C/2013 A1 (Siding Spring) 2013-08-15

[rogerg (Roger)]

C/2013 A1 (Siding Spring) from 2014-08-15.
1) 10x300s summed (as per normal)
2) 10x300s median, with DBE background gradient removal. Moon was at 67% which I think is where the additional gradients are still being introduced from.

Object: Comet C/2013 A1 (Siding Spring)
Date of Observation UT: 2014-08-15
Time of Observation UT: 16:11
Observer Name: Roger Groom
Location of Observation: Perth, Western Australia (-31o54'S, 116o09'E)
Camera: SBIG ST8-XME (bin 1x1)
Filter: Red Astronomik Type II (not Type IIc)
Exposure Time: 10 x 300 sec
Plate Scale: 0.84 arc sec/pixel
Position Angle: 0 degrees 26 minutes from North
Axes: North-up, East-left

I can't explain the well defined upper edge to the comet's outer area? See highlighted version. If I push the raw data enough it is there. I'm quite sure it's not flat/reduction related, but can't rule out interference from the moonlight and subsequent internal reflections?

Focusing failed again but there were two series of 10x300s which happened to be in reasonable focus, luckily. These images are derived from one of those series.

My webpage updated with the latest: http://rogergroom.com/astro-photogra...siding-spring/

[cometcatcher (Kevin)]

I think that edge at the top is real. This is just a weird shaped comet! These are excellent pics with moon present.

[rogerg (Roger)]

Originally Posted by cometcatcher

I think that edge at the top is real. This is just a weird shaped comet! These are excellent pics with moon present.

Yeah weird shape is about right ... it keeps changing shape more than I expect also.

[glenc (Glen)]

Thanks Roger for these detailed images.
The attached Guide 9.0 map shows the location of the mag 8 comet at midnight tonight with the zenith up.
The comet is 2.7 degrees below alpa Hyi, 7.5 degrees from Achernar and 14.5 degrees from NGC 104 = 47 Tuc.