Nice work with the 7D and the Sigma 17-70. I have one of those Sigmas in K-mount. It is a great lens.
Phil, these shots really stand out against the black of the night sky and something different from the average photos on the site, hopefully they will inspire others to try something similar,
It is always desirable to get it right in the camera first but there is nothing wrong with tidying up in Photoshop or similar programs. They make what we a doing a little more enjoyable.