How was the photon that hit my eye produced?

      How was the photon that hit my eye produced?       there are many ways that a photon be generated from an atom or a molecule. A planetary nebula is a cloud of gas surroundin" rel="nofollow">ing a glowin" rel="nofollow">ing star. Please see the accompanyin" rel="nofollow">ing photo for reference. The gas is comprised of molecules, but for the purpose of the assignment we can assume that they're just atoms with electrons. Photons leave the nebula and hit my eye, allowin" rel="nofollow">ing me to see it. Photons are also leavin" rel="nofollow">ing the star. How was the photon that hit my eye produced?