circadian

Everyday

To do with the body's natural daily clock, a cycle of about 24 hours that controls when we sleep, wake and feel hungry. tree →

In the lessons

In science and health lessons, circadian rhythms explain why we feel sleepy at night, why jet lag happens, and why screens before bed can keep us awake. Plants and animals have them too. Phrases: "circadian rhythm", "circadian clock".

Examples

• Your circadian rhythm tells you when to sleep. tree →
• Jet lag happens when your circadian clock is out of step with local time. tree →
• Bright screens at night can confuse your circadian rhythm. tree →
• Flowers that open in the morning follow a circadian rhythm. tree →
• Teenagers' circadian rhythms make them sleepy later at night. tree →

Note

Pronounced "sur-KAY-dee-un". From Latin "circa" (about) and "dies" (day): about one day, roughly 24 hours.