From: utzoo!decvax!harpo!seismo!hao!hplabs!sri-unix!Gloger.es@PARC-MAXC Newsgroups: net.space Title: Re: tidal forces Article-I.D.: sri-unix.4971 Posted: Sun Dec 19 09:33:51 1982 Received: Sat Jan 1 01:11:07 1983 Did I miss something? Actually look what up? If you just want to know how to compute gravitational tidal gradients, you start with the unit standard astrophysics equation, gravitational field strength = G*M/(d**2), and you take the first derivative with respect to distance to get the tidal effect, tidal gradient = 2*G*M/(d**3). And a quick check: The mass of the sun is 27 million times that of the moon, while its distance from earth is 390 times that of the moon. The above equation suggests that the sun's tidal effect at the earth compared to that of the moon will be 27,000,000 / (390**3) = 0.45, which is correct. It's because that specific result happens to come out within a small factor of one that earth has its strange dual solar/lunar tides.