Answer:
Kepler's third law - shows the relationship between the period of an objects orbit and the average distance that it is from the thing it orbits. This can be used (in its general form) for anything naturally orbiting around any other thing.
Formula: P2=ka3 where:
P = period of the orbit, measured in units of time
a = average distance of the object, measured in units of distance
k = constant, which has various values depending upon what the situation is, who P and a are measured.
This is the general form of the formula, so obviously you need at least two of the quantities to find the third. "k" is the trickiest thing since it depends upon the objects that are involved and how you measure "P" and "a". Since "P" can be measured in any unit of time (seconds, days, years, etc), and "a" can be measured in any unit of distance (meters, km, AU), the value of "k" can be quite diverse from one system to another.
There is a simplified version of this law: P2 = a3 where:
The object must be orbiting the Sun
P = period of the orbit in years
a = average distance of the object from the Sun in AU
This version is much more simple, since it has "k" = 1, so it is ignored when those units of measure are used.
