Solar System

Comet C/2012 F6 (Lemmon)

This image shows Comet C/2012 F6 (Lemmon) as it appeared on 28th January 2013. Although not a naked-eye object the comet was easily visible in my 12x80 finderscope under a full Moon.
I also imaged this comet on 26th and 27th January and it became noticeably brighter during these three days alone. This image was made with the data from 28th January as it showed the faint tail best. Clearly visible are both the thin straight gas tail and the more diffuse dust tail that is curving down towards the left below the gas tail.

The comet was moving quite rapidly against the background sky. I measured the movement to be roughly 5 arcseconds per minute. This causes a problem when stacking the data, because either the stars or the comet itself will appear trailed in the final image. To avoid this I had to combine four different stacks of the data. First I used SD Mask in Maxim DL to combine the luminance data aligned om the comet nucleus. This allows for an image of the comet alone and the stars are ignored due to their shifting positions from frame to frame. This was repeated for the RGB data. Then I did another stack aligned on the stars, both for L and RGB. So I ended up with an LRGB of the comet alone and an LRGB of the stars with a smudge from the trailed/blurred comet.
In short, I then combined these in Photoshop and selected the stars as a layer over the comet image in order to produce this final image where both the stars and the comet are aligned properly.

Click here to see a video showing the comet's movement across the sky

Image details:
Date: 28th January 2013
Exposure: LRGB: 59:6:6:6m, total 1hrs 17mins @ -26C
Telescope: 10" Serrurier Truss Newtonian f/5
Camera: QSI 683wsg with Lodestar guider
Filters: Astrodon LRGB E-Series Gen 2
Taken from my observatory in Auckland, New Zealand

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