Zenith equivalent airglow continuum radiance in the observed bandpasses according to Eq. (13). Data points are shifted by 25 Å steps to prevent them from being plotted over each other. The ESO SkyCalc yearly average residual airglow continuum (Noll et al. 2012; Jones et al. 2013), the X-shooter 2009–2019 mean airglow continuum (Noll et al. 2024), and the ZL spectrum above the atmosphere toward the ecliptic north pole (Meftah et al. (2018) solar spectrum scaled to Kelsall et al. (1998) model) are shown. Upper limits are derived in the 10 500 Å band and are indicated by arrows.