Original: Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution, Astronomical Journal, 118, 2430 The issue of how such a diverse range of nebular shapes can be produced is a controversial topic.
Simplified: Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution, Astronomical Journal, 118, 2430If they aren't close, there is not a good way to figure out how far away the are yet.