Hey there Steve - sure, thanks for asking.
You need to read up on 'stacking'. Its a common technique in astrophotography, where you place several frames (layers in potoshop), of the same scene on top of each other, register them exactly, and then average the pixel content through the layer stack in various ways. For instance Median or Mean values of each pixel stack. The result is that you get rid of random image noise and atmospheric haze, because these factors are random from image to image. I believe you need Photoshop CC to have access to Photoshops stacking functions, though it is possible to stack manually.
The more photos you stack, the cleaner the result generally. In this case, I used something like 240 frames off Magic Lantern Raw video. I could have shot 1000+ raw frames and chosen the best frames from that, but shooting video is way more practical in this scenario.