Reference: The 3-D ionization structure of NGC 6818 (the Little Gem): a planetary nebula threatened by recombination
Benetti et al. - A&A 400, 161 (2003)
The fixed image at the start of the movie corresponds to the nebula as seen
from Earth (North is up and East is left).
Each movie is about 150-250 Kby in size.
Rotation around the N-S axis
Rotation around theE-W axis