Re: Just to be sure: Planet with multiple moons

In article <48232c0d$0$15892$edfadb0f@[EMAIL PROTECTED]
>,
Peter Knutsen  <peter@[EMAIL PROTECTED]
> wrote:
>It is said that even Hal Clement effed up once, so I feel I ought to ask 
>in here, just to be sure:
>
>If a planet has multiple moons, all large enough to be visible, as 
>discs, from the surface (through the atmosphere), i.e. unlike the moons 
>of Mars, 

	From the surface of Mars, Phobos has a third of the angular
diamter of the Moon from Earth. I think even Deimos can be resolved with
the human eye. 

>will they all be in the same phase at the same time, i.e. full, 
>waning, new, waxing?

	No. 

	I think a sheet of paper and a pencil is all you need to see
why but this gif might do.

	http://en.wikipedia.org/wiki/Image:Orbits_of_Phobos_and_Deimos.gif

 	The phase is dependent on the angle between the observer on
the planet, the moon and the sun and since the moons take different 
periods to orbit their primary, the same fraction of their illuminated
surface usually won't be visible from the observer's POV. They will 
wax and wane according to their periods.

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