a rhythmically occurring cue given by the environment, such as a change in light or temperature, to reset the internal body clock.
look out for zeitstorers! the german words "zeitgeber" (time-giver) and "zeitstorer" (time-taker) are used by researchers to describe different cues in your environment that can affect your schedule. a zeitgeber, says frank, is an event or person that helps you maintain your routine — for example, a cat that should be let out at a given time or a spouse who must catch the same train daily. a zeitstorer, conversely, disturbs your routine, the way a business trip or overnight guests might. figuring out how to maximize the use of zeitgebers and minimize the effect of zeitstorers will ultimately help improve your sleep and mental health. everydayhealth.com
zeitgeber: an environmental agent or event that provides the cue for setting or resetting a biological clock. to be synchronized with our environment, we need the input of zeitgebers. the most important zeitgeber in nature is light. social factors, chemical factors and activity can also serve as zeitgebers. light is a so-called photic type zeitgeber, whereas activity, for example, is called a non-photic zeitgeber for the biological clock. medicinenet.com