ABSTRACT
Each of us has an internal mechanism, called a biological clock, which affects the biological and psychological processes that naturally vary over the 24-hour day. These processes are termed ‘circadian rhythms’ from the Latin ‘circa’ meaning about and ‘dias’ meaning day. So circadian rhythm means a pattern which varies on a cycle of approximately 24 hours. Examples of some of the processes are body temperature, hormone secretions, and alertness, but it is important to recognize that there are many more processes within us that vary coincident with our 24-hour day. There are a number of cues, called ‘zeitgebers’ (German for ‘time cues’) within the environment, which help keep these processes in sync, and when everything is in synch, we feel pretty good. Light is the primary zeitgeber which keeps the rhythms consistent (locked to a certain time of day) and in synchrony with one another, but there are other zeitgebers such as social factors (meals, work activity, etc.) which contribute to the stability of these internal processes as well.
