Jay and Daniel, You may be interested in this 2004 3D simulated mathematical construction of the Crab created from radial spectroscopy data - http://www.fiz.uni-lj.si/~vidrih/CrabNebulaSpectroscopy/movie.mpg The Crab is spherical with filaments extending from the center to an outer spherical thin shell. - Kurt Cadez, A., Carramiñana, A., & Vidrih, S. 2004, Astrophysical Journal, 609, 797-809, Spectroscopy and 3D imaging of the Crab nebula. http://arxiv.org/abs/astro-ph/0403153