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## Main Question or Discussion Point

hey, how to find the distance of two planets, say, earth and moon? i know it can done by apply equations of circular motion and gravitation, but it seems to me that there's always a piece of information missing.

like, mass of earth M :

mg = GMm/r^2

M = gr^2/G

u still need r to find M.

if u know what i mean.

thanks.

like, mass of earth M :

mg = GMm/r^2

M = gr^2/G

u still need r to find M.

if u know what i mean.

thanks.