Answer to Question #32425 in Astronomy | Astrophysics for Bernard

How correct is the measurement of the mass of planets and stars? There is no way we can know correctly how heavy are stars or even galaxies . Even the formula won't work cause we don't know the mass of moon to find the mass of earth . How can we prove how heavy is a mountain without knowing 100% the material and actual volume , measuring gigantic objects is impossible with our technology