Nuclear fusion reactions at the center of the sun produce gamma-ray photons with energies of order 1 MeV (106 eV ). By contrast, what we see emanating from the sun's surface are visible-light photons with wavelengths of about 500 nm . A simple model that explains this difference in wavelength is that a photon undergoes Compton scattering many times− in fact, about 1026 times, as suggested by models of the solar interior− as it travels from the center of the sun to its surface.