Figure 3.

Anatomy of a prototypical waveform with relevant terminology. The vertical axis represents some circadian function, e.g., the net activity level of a clock protein. Circadian phase refers to an organism’s status along the waveform; the phase can be shifted to a new circadian rhythm through a process called circadian entrainment. Phase shifts can occur in either direction; they can be triggered by light exposure, temperature, nutrient availability, exogenous melatonin, etc.