Mon Prof Augmenté
Moons and Planets in Orbit
A moon keeps falling toward its planet, but its sideways speed carries it around instead of into it. The same happens to a planet circling a star.
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Age 14: open this week
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In the picture
- The star at the centre: the body that holds the planet on its path
- The blue planet: a body circling the star
- The small grey moon: a natural satellite circling the planet
- The dotted loop around the planet: the moon’s repeating path
- The dotted loop around the star: the planet’s repeating path
Examples
- The Moon circling Earth about once every 27 days
- Earth circling the Sun once every 365 days
Key takeaways
- A natural satellite stays in orbit because it falls continuously while moving sideways fast enough to keep missing the body it falls toward.
- Every orbit balances gravity pulling inward against sideways motion carrying the body forward.
Carry on in the app
Three questions on this lesson. It has left the free week, so its quiz is for subscribers.
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