Moths will circle bright objects, and thus appear to be attracted to light. One hypothesis advanced to explain this behavior is that moths navigate by maintaining a constant angular relationship to a bright celestial light, such as the Moon. The Moon is so far away, that even after traveling great distances, the change in angle between the moth and the light source is negligible. However, when a moth encounters an artificial light and uses it for navigation, the angle changes noticeably after only a short distance. The moth instinctively attempts to correct the angle by turning toward the light, which results in a spiral flight path that gets closer and closer to the light source.
In 1972, Henry Hsiao, now professor of biomedical engineering, suggested that the reason for moths circling lights may have to do with a visual distortion called a Mach band [1]. Henry Hsiao conjectures that moths, as nocturnal creatures, fly towards the darkest part of the sky in pursuit of safety and are thus inclined to circle ambient objects in the Mach band region. This hypothesis is not scientifically accepted and has never been confirmed. It should be noted that many moths fly directly towards light source, which seems to contradict this hypothesis.
http://en.wikipedia.org/wiki/Moth#Attraction_to_light
Originally posted by AThousandYoungYawn...so if moths use the moon as navigation, how do they navigate when there is no moon? Or when it's cloudy at night?
Moths will circle bright objects, and thus appear to be attracted to light. One hypothesis advanced to explain this behavior is that moths navigate by maintaining a constant angular relationship to a bright celestial light, such as the Moon. The Moon is so far away, that even after traveling great distances, the change in angle between the moth and ...[text shortened]... eems to contradict this hypothesis.
http://en.wikipedia.org/wiki/Moth#Attraction_to_light