Kepler's third law:
Period squared is proportional to semi-major axis cubed.
This gives us our first equation of the semester (yippee!):
where P is the period,
a is the orbital distance
(called semi-major axis), and
where
Here is the complete form of this equation:
means "is proportional to."
where P is in seconds, a is in meters, and where M is the mass (in kg) of the object being orbited.
What is G?