Kepler's third law

9.0

A planet's orbit time squared increases with its average distance from the Sun cubed

noun
/ˈkɛplərz θɜrd lɔ/

Specialized

: tercera ley de Kepler

Using Kepler's third law, astronomers can calculate how long it takes a planet to complete one revolution around the Sun based on its distance.

Examples

A moon outside the ring orbits slower than the ring particles (Kepler's third law again).

Academic text (1995)
But I do ask them to understand Kepler's third law.

Academic text (1996)
According to Kepler's third law, the time it takes for a given ring particle to complete an orbit is shorter the closer the particle is to the planet.

Academic text (1995)
From these observations and Kepler's third law of planetary motion, students determine mighty Jupiter's mass.

Academic text (1996)
Once an absolute distance is known, Kepler's third law, p = a³, with a measured in AUs and P in years, can be used to figure the distances to all the planets and to the Sun. -- Louis Mayo

Academic text (2004)
According to Kepler's third law, the square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit.
To understand the motion of the planets, students learn about Kepler's third law, which relates a planet's orbit to its distance from the Sun.

Synonyms

harmonic law

vsKepler's third law

Specialized

9.9

A rule that relates a planet's orbit time to its distance from the sun

is the same law but phrased as proportionality between those quantities

Surface Forms

Kepler's third law singular

Kepler's third laws plural

Morphology

Kepler's + third + law

The structure 'Kepler's third law' clearly signals a named scientific law (possessive + ordinal + law), so a learner can infer it is the third law attributed to Kepler. However, the specific technical content (the precise mathematical relation between orbital period and semi-major axis) is specialized and cannot be derived from the constituent words alone, so full understanding requires domain knowledge.

Etymology

Kepler's third law comes from the work of the astronomer Johannes Kepler, who watched how planets move and found a neat number rule: the 'square' of a planet's time to go around the Sun matches the 'cube' of its distance from the Sun. So the law explains why the farther a planet is, the longer it takes to orbit.