[extropy-chat] Astronomical question

[BillK]

On Wed, 2 Mar 2005 23:22:25 -0800 (PST), Mike Lorrey wrote:
> 
> Yes, this is common knowledge, that solar tidal influence is about half
> that of the moon.
> 
> Are you also considering the tidal influence of the sun on the moon?
> Solar influence on the moon is so significant that the moon's off
> center center of gravity causes it to wobble detectably when it is
> ebbing. The moon's geometry is a bit warped...
> 
> Oh, and BTW: you shouldn't discount Jupiter either. I hear it's
> influence is something like 1% of lunar tide. Not huge, but its there.
> 

Bit of confusion creeping in here. Gravitational effect does not equal
tidal effect.

Gravitational effect depends on the square of the distance.
Tidal effect depends on the *cube* of the distance. 

See: <http://www.badastronomy.com/bad/misc/planets.html>
(If you go to <http://www.badastronomy.com/> and search on 'tides' you
get lots of interesting articles)

Planet        Mass        Distance           Gravity             Tides
               (10^22 kg)                         (Moon=1)         (Moon=1)
Mercury        33              92               0.00008           0.0000003
Venus         490              42               0.006              0.00005
Mars             64              80               0.0002            0.000001
Jupiter   200,000            630               0.01               0.000006
Saturn     57,000          1280               0.0007            0.0000002
Uranus      8,700          2720               0.00002          0.000000003
Neptune   10,000          4354               0.00001          0.000000001
Pluto              ~1          5764              0.0000000006  0.00000000000004
Moon            7.4               0.384         1.0                 1.0

This is using the distances of closest approach to the Earth to
maximize the effect. Realistically, the force will be smaller than
what is listed.

See my previous posts for formulae for calculations.

BillK