= Solution
For the two-body approximation with a dominant central mass, <Kepler's laws of planetary motion> are:
* <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>, $T^2=4\pi^2a^3/(GM)$ 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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