planetary nebulae
esiegel | October 11, 2012"A colour is a physical object as soon as we consider its dependence, for instance, upon its luminous source, upon other colours, upon temperatures, upon spaces, and so forth." -Ernst Mach
Our Sun, like all Sun-like stars, will come to the end of its life someday. All the hydrogen fuel in its core will eventually burn up, and when this happens, the core itself will begin to contract. When temperatures are finally high enough, the end product of hydrogen fusion -- Helium-4 -- will begin to fuse in the contracted core, and the Sun will expand into a Red Giant.
Image credit: Northwestern…