What causes Earth to have day and night?
AnswerEarth spinning on its axis
As Earth rotates, each place turns toward the Sun for daytime and away from it for night.
Challenge · Facts & stats
3 Day facts & stats
7 fact-checked facts about three-day habit sprints and the science of days and habits, each with the reason behind it. 5 more are in today's round and join this page after it closes.
The basics
How many days are in a leap year?
Answer366
Leap years add February 29 to the calendar, giving 366 days.
Going deeper
In habit science, the 'habit loop' is usually described as cue, routine and what?
AnswerReward
A cue triggers a routine, and a satisfying outcome makes the brain more likely to repeat it next time.
A 2009 University College London study found new habits took a median of about how long to become automatic?
Answer66 days
Participants took between 18 and 254 days to make a behavior automatic, with a median of about 66 days.
What is the body's roughly 24-hour internal clock called?
AnswerCircadian rhythm
'Circadian' comes from the Latin circa diem, meaning 'about a day'.
Expert level
Which planet takes longer to spin once on its axis than to orbit the Sun?
AnswerVenus
Venus takes about 243 Earth days to rotate once but only about 225 Earth days to go around the Sun.
Measured against the distant stars, how long does Earth take to spin once (a sidereal day)?
AnswerAbout 23 hours 56 minutes
Relative to the stars Earth turns in about 23 h 56 min; a solar day is longer because Earth also moves along its orbit.
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