Fig. 1: The black line shows the background model in the optical for 3 days from new moon and a resolution of R = 1000 (no site or airmass dependence). The dotted red line represents the continuum (which is assumed to be constant in each band). For comparison, the faint grey line shows an optical background model from the Gemini Exposure Time Calculator for Mauna Kea and for a moon phase of 7 days from new moon. To match this model's photon flux in the V-band with our model we need to select a moon phase of 10 days from new moon, which is shown as the blue line.