**Circadian Rhythm** refers to the synchronization of biological entities (such as ourselves) to the daily sunrise & sunset cycle. All organisms we've tested with lifespans longer than a few days have a circadian rhythm. This was originally discovered when a sun-tracking plant was kept in a box, and it was found to continue to open & close its leaves during the times it should, despite not having access to the sun to signal it. > [!note] Circadian means "about a day", **not** exactly 24 hours Your circadian rhythm is generated by your suprachiasmatic nucleus (located in the hypothalamus). It is not precisely 24 hours. Its natural length is typically *slightly more than 24 hours* and varies from person to person. [[Sunlight Exposure]] corrects for this imperfection. Circadian rhythms have behavioral (e.g. feeling sleep) and physical (e.g. body temperature) components. **** # More ## Source - [[Why We Sleep]]