the value of the missing variable.
Kepler’s first law: Every planet moves in an elliptical orbit with the sun at
one focus of both of them in an ellipse.
Kepler’s second law: A planet moves faster when it is closer to the sun than
when it is further away.
Kepler’s third law: The ratio T^2 /a^3 is the same for all the planets, where T is
the time it takes the planet to make one orbit (the period) and a is the length of
the semimajor axis of a planet’s orbit.