The animation is composed of images that were used for the optical navigation campaign, as Rosetta followed (2867) Steins, refining its trajectory to close in on the asteroid. They were taken once a day by Navigation camera A, between 25 August and 3 September.
The images have been adjusted so that the stars are of roughly the same brightness from day to day, although the exposure times decrease and Steins becomes brighter as Rosetta appoaches.