Terrestrial water-vapor lines in the CN-line region near 8000 Å for the Sun (top) and the solar-twin 18 Sco (bottom; shifted by –0.15). The PEPSI spectra are shown as dots. The solar spectrum is compared with the IAG FTS atlas (the deep-lined spectrum in red) and the “dry” NSO FTS atlas (weaker lined in blue). The IAG FTS spectrum is contaminated by very strong telluric lines while the NSO spectrum is comparably more noisier. Note that the 18 Sco spectrum was shifted to match the solar spectrum.