Here is a compilation of my key observations of a comet C/2013 US10 (Catalina). Pictures were taken on 8 Dec 2015; 29 Dec 2015 and 6 Feb 2015 (left to right): I tried to catch clear sky (this winter is extremely cloudy). Place: Kyiv (Osokorky district).
All images are on the same scale, a size of each picture is 2x2 arc degree (approximately four angular diameters of the Moon).
Black-and-white version:
Initial color version:
Two tails of the comet have different nature: straight upper tail (in the first and the second images) is gas ion tail, it points to a direction opposite to the Sun (ions are pushed back by solar wind and light pressure); the other curved tail is of dust, it is more affected by Sun's gravitation and is left behind in the comet's orbit.
The distance between the comet and the Sun increases from the first to the third picture (while distance between the comet and Earth for the second picture is less substantially than for the first and somewhat bigger than for the third): the comet's activity decreases, only the dust tail is revealed in the last image.
To make the photos, I used Canon EOS 600D with EF 50mm F/1.8 II lens on fixed tripod. Images were captured and processed in different conditions: there were 100x3s, 260x4s, and 210x12s individual frames averaged for the first, the second, and the third images respectively.
While processing, stacking by comet position was used. Stars in the first picture are affected by Earth's rotation (or, partially, optical distortion of the lens) while on the next two pictures star trails arose because of comet's own movement (remember that I stacked images using comet's position as a reference).
Finally, I made an animation from a set of frames captured during the third session. Here is comet's own movement during approximately an hour (57 min).
