I think it may be related to the sun, but I don't understand the "tooth" shape in the GIF - is this a shadow of something? Is the spacecraft already spinning for the satellite deployment?
What are the sources of light. Possibly some combination of Sun, Earthshine, infrared/red thermal radiation from the nozzle, but is there also artificial illumination from the spacecraft for the camera?
I can't understand exactly what I'm looking at here (the mechanism making this pattern of light on the nozzle).
Full video shown here - use the launch time code T+ 00:26:30 to 00:28:30 for reference.
above: Early illustration of a 2nd stage, shown without a large communications satellite payload from the Spaceflight 101 article Falcon 9 v1.1 & F9R Launch Vehicle Overview. The dimension listed there as about 3.7m x 13.8m without payload adapter. This is for reference only.