Reference: The 3-D Ionization Structure and Evolution of NGC 6720, the Ring Nebula
C.R. O'Dell, F., Sabbadin & W.J. Henney, A.J. in press
The Ring Nebula has been observed by C.R. O'Dell and W.J. Henney at the Observatorio Nacional en San Pedro Martin (UNAM) using the MEZCAL spectrograph mounted at the 2.1m telescope (24 position angles for [OIII], Halpha and [NII], and 6 position angles for HeII).
The fixed image at the start of the movie corresponds to the nebula as seen from Earth (North is up and East is left).
Rotation around the N-S axis