Prompted by a tweet by NSHipster, and a subsequent thread, I wanted to find out how Mojave dynamic wallpapers worked. NSHipster and ole reverse engineered the file format. In the Twitter thread, NSHipster mentions an edge case: What happens above 66ºN (latitude)?
The first thing to do was find out what process handles the wallpaper on macOS. I primarily do iOS research, and honestly had no idea. I opened Console, searched for "solar", and then changed my static wallpaper to a dynamic one. Voila!
Message: index: 7 next: 14815.999366
Process: Dock