Blind clocks reveal elusive light input pathway in Drosophila

Circadian clocks run too fast or too slow relative to the 24-hr period of the solar day. For this reason, biological pacemakers rely on the cyclic nature of the environment to entrain their oscillations. Such environmental cues, when used as a reference for the time of day, are called Zeitgebers or time givers, and an understanding of how such cues impinge on the circadian pacemaker is crucial for our understanding of biological timekeeping.