Comparison of the spectrum components in the O₂ A-band. The top spectrum is the observed spectrum during umbral eclipse with all components in it. The next lower spectrum is the solar plus the telluric component obtained from a smoothing-spline fit to all spectra versus air mass and time. The two bottom spectra are the ratio and the difference of above, respectively, and reveal the Earth’s transmission spectrum. A vertical offset of 1.3 is applied for better visibility. Wavelengths are in Ångstroem. We note that the ratio spectrum is plotted with dots in order not to overemphasize the many divisions by nearly zero.