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Re: CONCULTURE: dual planets

From:Simon Richard Clarkstone <s.r.clarkstone@...>
Date:Wednesday, November 17, 2004, 23:44
Everybody note:
I have cross-posted this to both ConLang and ConCulture.  The former
list started it, but I feel the latter list is also appropriate.

Wesley Parish wrote:
> First things first - I think the tidal effects are going to be ginormous. This > will effect the crust as well as the liquid surface.
Note this when considering the rest of my response. [snip]
> As far as I can see, the day would be longer, because both planets, if close > enough to be a double planet, would be tidally locked to each other. That's > inescapable. At the proper distance - which I used to know but have since > forgotten - the orbit would decay at much the same pace as the Earth-Moon orbit.
Actually, the only reason that our Moon's orbit is decaying (note: orbit is getting _larger_ as it decays) is that it is using energy to power the tides in Earth's atmosphere, seas, and crusts. (Yes, there _are_ small tides in the crust. Particle physicists, of all people, need to know this to use large accelerators properly.) This also means that Earth's days are getting longer, as its rotational energy is helping to cause tides to move. However, if two bodies are tidally locked (e.g. Pluto and Charon), the orbital distance will not change (if their orbits are elliptical, tides will tend to make them more circular), and the planets will have the same view of each other in the same place in the sky all the time. The view will change slightly (I think) if orbits are not exactly circular, because the orbital angular velocity is varying, but the rotational angular velocity is much more constant. -- Simon Richard Clarkstone*rkst*n* / s*m*n_cl*rkst*n*


John Cowan <jcowan@...>