Some of the most gorgeous, ghostly, and variable objects in the universe are planetary nebulae.  They are all formed in a similar process, as a low-mass star (like our Sun) sheds it’s outer layers of gas and dust, heating them to a glow as they disperse over hundreds of millions of years.  A few Billion years from now, the Sun will undergo the same major state change.  When this happens, perhaps other species in the far future will gaze upon it and marvel at its beauty. One of the difficulties in studying a planetary nebula is measuring it’s distance from...