The moon appears to change size, shape, and angle throughout the lunar cycle. Furthermore, the lower the moon's angle, the less useful illumination it provides. It's important that leaders keep this in mind when planning night operations. Movement toward a highly illuminated moon located low on the horizon can be extremely hazardous when NVGs are in use. Not only can the brightness degrade the NVG image, deep shadows cast by the moon may hide hazards that even NVGs can't see.
Stars provide much of the illumination NVGs see on moonless or low illumination nights.
The newer NVGs perform best under these starlit nights. In addition, solar illumination is present for the very short time that the sun is within 12 degrees of the horizon after sunset and before sunrise. Too much solar illumination, however, can also degrade NVG resolution. Other natural sources such as northern lights and zodiacal lights are also sometimes present, but they're not reliable illumination sources. Manmade sources of illumination Illumination from cities, fires, vehicles, and flares can have enormous effects on NVG performance.