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Not bad Deeno, a good attempt for your second shot.
It's a little on the soft side but you'll get better focus and better tracking/polar alignment with more experience.
Darks are applied to each frame in order to subtract away the noise that is present in each frame. This is done by taking a separate set of dark frames by covering the front of the lens and taking an exposure identical to the normal frame.
Same length of time and same ISO and preferably around the same ambient temp.
This records only the noise of the exposure which then is subtracted from each light frame to produce a cleaner image.
Flat frames are created and applied to the light frames to eliminate any 'defects' within the optical train you are shooting through, ie: your scope or lens system.
This is done to remove vignetting, dust shadows etc and is achieved by shooting at a light box which has an even illumination or a white t-shirt covering the optics or a clear pre-dawn sky to give you a frame that will show up these 'defects'.
This becomes your flat frame which you apply to each exposure to 'flatten' the light frames and remove these 'defects' that the optics themselves produce.
In flat frames the exposure is different to your light frames but it is imperative to keep your optical setup the same as what you shot your light frames through.
In other words, you don't change your camera orientation on the scope or remove anything within the light path of your setup.
I hope this explains it a little, I can run through it with you a little better when I see you at the pony club.
I know it sounds complicated but once you get the hang of it, it's well worth applying to your images for a better result.
Also I highly recommend shooting in Raw as you will have a much better dynamic range to play with when adjusting your levels etc in the final image and not loose valuable data in the process.
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