Sunday 19th October 2014 Mars meets Comet Siding Spring

The comet C/2013 A1 Siding Spring made a very close pass to the planet Mars at 18:28 U.T.  (Universal Time). I took a series of 10 second  images starting at 19:11 U.T. i.e. 43 minutes after its closest distance from Mars of 87000 miles. The problem was that Mars was at magnitude  0.87 and the comet was at magnitude 8.52 so a magnitude difference of approximately 8 magnitudes  - which meant that Mars was around 600 times brighter than the comet making it rather a photographic challenge. Also at the time of my first image Mars and Siding Spring were only separated by 2 minutes 15 seconds of arc! (About one fifteenth of the diameter of the full Moon.)

 Also my CCD camera does not have an anti-blooming gate and to detect the comet I needed to heavily over saturate Mars which meant that large spikes indicating an overflow due to the bright planet would get in the way of the comet image - which they did!

The other factor was that the encounter was not long after sunset and the low altitude of the event. The altitude of the comet was 12 degrees 30 minutes when I started - dropping by a degree every 8 minutes or so. The initial Air Mass - a measure of the thickness of the atmosphere the light has to penetrate -  was 4.57 and it soon reached 10! Ideally it should be 1.

I targeted the comet using my SkyX software as shown below. I knew the angle that my camera was sitting at with respect to North so I was able to superimpose a Field of View indicator as shown. This chart should now correspond exactly to the image taken.

 This is the first image taken at 19:11 U.T. 

 The star just above and to the right of the comet is UCAC3 131:242659 (from chart).

If you check this on the image there is a direct correspondence.

 The animation below shows the comet moving away from the planet and Mars moving from left to right in its orbit. The images deteriorate as the animation progresses -  eventually the mountain edge crosses the image and the objects set.