The nebula patterns and brightness slowly changes over months and years from shadows of dust clouds illuminated by the star R Monocerotis, which in itself encased in a dust cloud. Discovered by William Herschel, and studied by Edwin Hubble who it is named after.
An animated sequence of yearly images of the nebula, how much is due to different processing and different scopes and camera I don't know, but changes are visible in the nebula.
