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Re: Yes, I'm back

From:Andreas Johansson <and_yo@...>
Date:Tuesday, January 21, 2003, 17:15
John Cowan wrote:
>James Landau wrote: > > (This leads to another question: is there anyone here who knows > > how to find out how fast a planet will rotate on its axis or complete a > > year, given its volume, mass and distance from the sun?) > >The parameters of mass/volume, day length (rotation on axis), and year >length (revolution around sun) are absolutely unrelated. The year >length is related to the distance from the sun by the following >relationship (Kepler's 3rd or harmonic law): Y^2 = D^3, where Y is >measured in years and D is measured in astronomical units (Earth's >distance from the sun, about 150 million km).
The rotational periods of Earth, Mars, Jupiter, Saturn, Uranus and Neptune are all in the 9-25h range. The much longer rotational periods of Mecury and Venus are likely due to tidal slowing caused by their proximity to the Sun. This has caused atleast some astronomers to conclude that this order of magnitude is "natural" for the rotational period of a terrestrial or jovian planet. There's also apparently a tendency for the period to go down as the planetary mass goes down. Pluto's period of about six Earth days represents locked orbitation with its satellite Charon. But Pluto doesn't count anyways, it being a Kuiper object rather than planet comparable to the terrestrials or jovians. Andreas _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE*