 In recent years, however, observations made using the Hubble Space Telescope have allowed a new method of determining distances called expansion parallax. As we know, all planetary nebula are expanding, and observations taken several years apart with high enough resolution can reveal the angular growth of the nebula in the plane of the sky. Using the Doppler effect to approximate the velocity of the expanding material, we can calculate the distance the nebula expanded. With that, simple math gives us the distance to the cat's eye. 3,260 light years.