Posted by Megan on .
From your intergalactic survey base, you observe a moon in a circular orbit about a faraway planet. You know the distance to the planet/moon system, and you determine the maximum angle of separation between the two and the period of the moon's orbit. Assuming that the moon is much less massive than the planet, explain how you can determine the mass of the planet.

Physics 
Elena,
G•M•m/r² = m•v²/r
v =2•π•r/T
G•M•m•/r²= 4• π²•m•r/T²
M = 4•π²•r³/G•T²
Since r and R are very large r = R•θ,
where R is the distance to the system and the θ is an angle separation