lew@ihlpa.UUCP (Lew Mammel, Jr.) (04/13/85)
It's been noted that the sun's tidal force (on the earth) is less than the moon's. Here's an interesting way to see this. The magnitude of the tidal force is proportional to m/r^3, where m is the mass of the tide-producing body and r is its distance from earth. If we divide top and bottom by R^3, the radius of the body cubed, we see that: F ~ rho * theta^3 where rho is the density of the body and theta is its apparent angular diameter. Since the sun and moon have equal apparent diameters, the ratio of their tidal forces on the earth is just the ratio of their densities. This also gives an easy way to estimate the tidal influences of the planets on the earth. (remember the Jupiter effect?) Lew Mammel, Jr. ihnp4!ihlpa!lew