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.
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