Humans, like many terrestrial organisms, are able to correctly perceive the time of day without knowing the position of the dial on the clock or the location of the sun. In association with this perception we experience oscillations in physiological parameters in time with the revolution of the planet on its axis. While these changes are often too subtle to be easily recognized, they are essential to the proper functioning of our bodies. When these cycles are perturbed, it can strongly affect our day to day lives as well as our extended medical outlook.