Scientists Say: Circadian

There’s a word for something that rises and falls in 24-hour cycles


We may wish to stay alert while we travel, but our circadian rhythms often demand that we sleep once it is late at night.

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Circadian (adjective, “Sir-KAY-dee-in”)

A period of about 24 hours. Rhythms that vary over a 24-hour period are described as circadian. Our sleep schedules are circadian. Similar 24-hour rhythms are found in other animals as well as plants, fungi and even bacteria.

In a sentence

When we stay up late reading on a brightly lit device, the light and late hours may mess with our circadian rhythm and disrupt our sleep.

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Power Words

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circadian  Recurring naturally on a 24-hour cycle.

circadian rhythm  Biological functions such as body temperature and sleeping/waking times that operate on a roughly 24-hour cycle.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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