The circadian pacemaker synchronizes to the Earth's rotation by tracking step-by-step changes in illumination that occur as the sun passes the horizon. While twilight progressions of irradiance and colour are considered important stimuli in this process...
Negelspach, D. C. (Creator), Kaladchibachi, S. (Contributor), Fernandez, F. (Creator) (2018). Raw phase-shifting data from The circadian activity rhythm is reset by nanowatt pulses of ultraviolet light. The Royal Society. 10.6084/m9.figshare.6820826.v1