Trails from multiple exposures
Notice the aircraft and satellite trails.
This image has been produced by a computer program (app)* that has added the 70 images together, simply on top of each other, keeping the brightest version of every pixel as it appears in all the images. The trails are therefore more pronounced than before and things which occur only in single frames (the aircraft and satellites) are also strongly presented rather than being watered down by averaging.
* My own GRIP program, which will be described later.