- Kepler's first law: a bound planetary orbit is an ellipse with the central attracting body at one focus.
- Kepler's second law: the line from that focus to the planet sweeps equal areas in equal times, equivalent to constant areal velocity.
- Kepler's third law: the squared orbital period is proportional to the cube of the semi-major axis, when the orbiting mass is negligible.
The first law includes a circular Kepler orbit as a special case. The third-law constant is the same for bodies orbiting the same dominant mass.
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