Mon Prof Augmenté
Planet Orbit Around a Star
Age 18 · Physics
A planet moves around a star on an oval path, with the star at one focus. Shaded wedges show equal areas swept in equal times, and a smaller inner orbit shows how orbit size and period are linked.
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In the picture
- The star at one focus: the body the orbit bends around.
- The large oval path: the planet’s orbit around the star.
- The narrow amber wedge near the star: area swept in a short time close to the star.
- The wide amber wedge far from the star: the same area swept in the same time farther away.
- The smaller inner oval path: a tighter orbit with a smaller size and a shorter period.
Examples
- A satellite speeding up as it passes near Earth and slowing as it moves far away.
- A comet racing through the inner solar system and lingering in the outer dark.
Key takeaways
- Orbits are ellipses with the central body at one focus.
- Equal areas are swept in equal times, and period squared scales with orbit size cubed.
Quiz: Planet Orbit Around a Star (Age 18)
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According to Kepler’s laws, what shape does a planet’s orbit around a star have?
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What does the equal-area rule say about a planet in orbit?
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How is a planet’s orbital period related to the size of its orbit?
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