LearnMechanics & orbitsBuilds on the rest
Orbital resonance
Two orbiting bodies exerting regular, repeating gravitational tugs on one another because their periods form a ratio of small whole numbers.
Why it matters
Resonance both builds and destroys. It keeps Io, Europa and Ganymede locked at 4:2:1 and keeps Io molten; it also cleared the Kirkwood gaps in the asteroid belt.
In practice
Watch the Galilean moons in this site's planetarium over a few simulated days — Io laps Europa exactly twice per Europa orbit, every time.
Rests on
- Kepler's lawsOrbits are ellipses with the Sun at one focus; a planet sweeps equal areas in equal times; and the square of the period is proportional to the cube of the semi-major axis.
- TidesThe stretching a body feels because gravity pulls harder on its near side than its far side.
4 concepts in the full chain back to first principles.
Leads to
Nothing here builds on it yet.