What is 'image stacking' and how can I apply it to my astrophotography to create better looking photographs? Are there any 'must have' resources for learning how to image stack for the purposes of astrophotography?
Image stacking is the technique of merging multiple images of the same object, and processing it in a way that increases resolution, decreases noise and artifacts, and multiplies the brightness of any single image. What this means in astrophotography is that, instead of taking one enormously long exposure (which will be susceptible to noise from the camera as well as resolution and trailing issues), you can take multiple small exposures and then stack them on top of each other to produce an image that has good brightness, contrast, and resolution. This article goes into more detail.
There are numerous pieces of software that can do this. One that is free, and is used very often by amateur astronomers, is Registax.