The Helix Nebula, also called NGC 7293, is a natural wreath surrounding a dying star. This breathtaking image of the Helix Nebula was captured by NASA’s Spitzer Space Telescope. The Helix Nebula is ...

In this image from NASA's Spitzer Space Telescope, "cometary knots" on the Helix Nebula show blue-green heads caused by excitation of their molecular material from shocks or ultraviolet radiation.