Solar flux at 1 AU as a function of wavelength (lower horizontal axis) and radial velocity between the observer and Sun (upper horizontal axis). The green line with a narrower line width has an FWHM of 0.0016 nm which was reported by Kumar et al. (1973). The broader, purple line has an FWHM of 0.015 nm as reported by Wilhelm et al. (1997). Since the two solar spectral fluxes integrated along the wavelength are assumed to have the same total photon fluxes in our model, the flux with the line width of 0.015 nm shows a lower peak than that with 0.0016 nm. The flux with the line width of 0.015 nm is multiplied by a factor of ten in this panel for scaling.