Top: All-sky image for an East–West synthetic aurora spanning the sky at 45° elevation Northward. The red curve shows the pointing direction of the instrument along a 45° almucantar. The radiance of the aurora (in yellow) is 100 nW/m²/sr, against 10 nW/m²/sr for the background. Bottom: Almucantar under a synthetic aurora. Comparison using different albedo curves from Figure 3. In black: no albedo. Other colors match the profiles shown in Figure 3. Azimuths are indicated with respect to the Northern direction, positive eastward.