"A circadian rhythm (/sərˈkeɪdiən/), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours.[1] It can refer to any process that originates within an organism (is endogenous) and responds to the environment (entrained by the environment)."

"The term circadian comes from the Latin circa, meaning "around" (or "approximately"), and diēm, meaning "day". Processes with 24-hour cycles are more generally called diurnal rhythms; diurnal rhythms should not be called circadian rhythms unless they can be confirmed as endogenous, and not environmental"

#todo How can I use https://en.wikipedia.org/wiki/Circadian_rhythm#/media/File:Biological_clock_human.svg to my advantage. Atleast I finally know why we don't shit in bed.

Criteria

1. The rhythm has an endogenous free-running period that lasts approximately 24 hours.
   1. The period of the rhythm in constant conditions is called the free-running period and is denoted by the Greek letter τ (tau)
2. The rhythms are entrainable.
3. The rhythms exhibit temperature compensation

Referenced in:

• tau
• Waking-up-early