Equations · equation

Kepler's Third Law

Celestial Mechanics · 1619

Equation: T² = 4π²a³ / GM
Field: Celestial Mechanics
Named After: Johannes Kepler
Symbols: T orbital period · a semi-major axis of the orbit · G gravitational constant · M mass of the central body
Year: 1619

Significance

Orbital period squared scales with orbit size cubed — the harmony that let Newton reverse-engineer the inverse-square law, and how we weigh stars, planets, and black holes today.

Minerals

Timeline

The Solar System Forms

Celestial Objects

Sun

Theories

Newtonian Mechanics Heliocentrism

Related

Law of Universal Gravitation Hohmann Transfer

Instruments

Keck Observatory Large Synoptic Survey Telescope (LSST)

Constants

Solar mass Newtonian constant of gravitation

Requires

Law of Universal Gravitation Centripetal Acceleration

Referenced by

constant

Newtonian constant of gravitation Solar mass

equation

Centripetal Acceleration Hohmann Transfer Law of Universal Gravitation

event

The Solar System Forms

instrument

Keck Observatory Large Synoptic Survey Telescope (LSST)

theory

Heliocentrism Newtonian Mechanics

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From the Equations database in Notion, last edited 2026-08-18. This page is the row, rendered by the build; nothing on it is written by hand.