设
为M、月球质量为m、月地间距离为r
GMm/r^2=m(4π^2/T2^2)r 得 T2^2=4π^2r^3/GM
如果地月看成双星,
半径为r2、月球轨道半径为r1,
r1+r2=r
GMm/r^2=m(4π^2/T1^2)r1.(1)
GMm/r^2=M(4π^2/T1^2)r2.(2)
由(1)(2)得,mr1=Mr2,又r1+r2=r
r1=Mr/(M+m).(3)
(3)代入(1),G/r^2=(4π^2/T1^2)r/(M+m) 得T1^2=4π^2r^3/G(M+m)
所以,T2^2/T1^2=(M+m)/M