hello everyone, I have a couple of questions from my astonomy course that are confusing me. 1. Which do you think would cause the larger error: a 10% error in "p" (period of orbit) or "a" (length of semi-major axis in units)? I would think that the "p" would produce the larger error, because it could alter the position of planet. Is that right? 2. The orbit of earth's moon has a period of 27.3 days and a radius (semi-major axis) of 2.56 x 10^-3 A.U. (=3.84 x 10^5 km). What is the mass of Earth? What are the units? Show your work? I'm not sure which formula to use, can anyone give me some pointers? Thanks a bunch.