David Buck wrote:

> Um, yea :-).
> 
> The star (Delta Pavonis) is about 20 lightyears from our Sun.  I don't 
> think a planet could orbit a star at a distance of 20 light years.

v^2/r = Mg/r^2 relates orbital speed to distance and solar mass.  v = 2 pi r / tau,
where tau is the orbital period, so 4 pi^2 r / tau^2 = M g / r^2 =>

tau = 2 pi * sqrt(r^3 / M g)

The Earth's orbital radius is 1.58e-5 light years.  20 light years is a factor 1.26e6
larger.  For comparable solar mass, this would yield an orbital period of 1.4 billion
years.  The age of the universe is 13.7 billion years.  So classically there's been
time for at least a few such orbits...

The problem is there could be no massive objects of comparable mass to the star within
the neighborhood defined by the length scale of the orbital radius, for example within
100 light years, or the orbit wouldn't be stable.

Dan

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gvdeynde <gvd### [at] gmailcom> wrote:Do you know of a site or
> reference work where I could get approximate data (good enough for this
> purpose of an educational animation) for the astronomy data?

It's good for a lot more than rough approximations, but to the best of my
knowledge, ephemeris data is the definitive source:

http://eclipse.gsfc.nasa.gov/TYPE/TYPE.html

You might try searching for interactive simulations too.  I know I've seen
models you can fly around in before, but I can't remember the name.

 - Ricky

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Hi all,

Thanks to all for your input.

David, yes, if you don't mind, I would like to have a look at your code.

Stephen, great simulation. Any chance of sending me the Bishop3d 
file/PovRay file?

all the best,
gert

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On Thu, 08 Jan 2009 09:36:04 +0100, gvdeynde <gvd### [at] gmailcom> wrote:

>
>Stephen, great simulation. Any chance of sending me the Bishop3d 
>file/PovRay file?

I'll just have to cut down the sizes of the image maps, they total about 6 megs.
The Bishop3D file is only 2K, zipped.
-- 

Regards
     Stephen

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gvdeynde wrote:
> Hi all,
> 
> Thanks to all for your input.
> 
> David, yes, if you don't mind, I would like to have a look at your code.
> 
> Stephen, great simulation. Any chance of sending me the Bishop3d 
> file/PovRay file?
> 
> all the best,
> gert
> 
> 

See the article "Delta Pavonis Celestial Mechanics" in 
povray.binaries.scene-files.

David Buck

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Alain wrote:
> Jérôme M. Berger nous illumina en ce 2009-01-07 15:13 -->
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> clipka wrote:
>>> David Buck <dav### [at] simberoncom> wrote:
>>>>   It was for a science fiction story I was working on that takes place
>>>> on a planet that orbits a star 20 lightyears away.  This is actually a
>>>> binary planet where two approximately equal mass planets orbit each
>>>> other (or around the center of mass of the two planets) and both orbit
>>>> the star.  The two planets are tidally locked to each other.  I wanted
>>>> to discover the dynamics of this world.
>>> Out of curiosity: Would such a system actually be stable in reality?
>>>
>>     It is: look at the Pluto-Charo pair of planets (planetoids?) in the
>> solar system.
>>
>>         Jerome
>>
>> PS: Of course, Pluto and Charo aren't 20 ligth-years away from their
>> sun, but that's probably just me being obtuse ;)
>>
>>
> It's 20 lightyears away from HERE.
> 
	I know that's what he *meant*, hence the smiley and the second part
of my sentence, but that's not what he *wrote*...

		Jerome
- --
mailto:jeb### [at] freefr
http://jeberger.free.fr
Jabber: jeb### [at] jabberfr
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On Thu, 08 Jan 2009 09:50:45 +0000, Stephen <mcavoysAT@aolDOTcom> wrote:

>On Thu, 08 Jan 2009 09:36:04 +0100, gvdeynde <gvd### [at] gmailcom> wrote:
>
>>
>>Stephen, great simulation. Any chance of sending me the Bishop3d 
>>file/PovRay file?
>
>I'll just have to cut down the sizes of the image maps, they total about 6 megs.
>The Bishop3D file is only 2K, zipped.

Bishop3D file
http://www.geocities.com/mcavoys/Bishop3D/Earth02K_4.zip

Image maps for B3D file.
http://www.geocities.com/mcavoys/Bishop3D/Maps.zip

If you unzip both files into the same directory and add that directory to the
PovRay library path it should work (I tested them) Any problems just ask either
here of at the Bishop3D forums
-- 

Regards
     Stephen

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Stephen nous illumina en ce 2009-01-08 15:05 -->
> On Thu, 08 Jan 2009 09:50:45 +0000, Stephen <mcavoysAT@aolDOTcom> wrote:
> 
>> On Thu, 08 Jan 2009 09:36:04 +0100, gvdeynde <gvd### [at] gmailcom> wrote:
>>
>>> Stephen, great simulation. Any chance of sending me the Bishop3d 
>>> file/PovRay file?
>> I'll just have to cut down the sizes of the image maps, they total about 6 megs.
>> The Bishop3D file is only 2K, zipped.
> 
> Bishop3D file
> http://www.geocities.com/mcavoys/Bishop3D/Earth02K_4.zip
> 
> Image maps for B3D file.
> http://www.geocities.com/mcavoys/Bishop3D/Maps.zip
> 
> If you unzip both files into the same directory and add that directory to the
> PovRay library path it should work (I tested them) Any problems just ask either
> here of at the Bishop3D forums
Just unzip in a sub-folder of the POV scene folder. No need to add any new path 
this way.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you have ever brought your 
computer to its knees by mistakenly launching 64 simultaneous frames to be 
traced, while trying to maximizing the benefits of parallelizing them.
Carsten Whimster

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Among other things, triple_r saw fit to write:

> You might try searching for interactive simulations too.  I know I've seen
> models you can fly around in before, but I can't remember the name.

Slightly off topic...

Has anyone seen a picture (ideally a photograph) of how a lunar eclipse
looks from the Moon (from there, it would be a solar eclipse). In total
lunar eclipses the Moon usually gets a reddish tint, apparently from
sunset-like light all around the Earth (as seen from the Moon), I'd like to
see this.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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Jellby wrote:

> Has anyone seen a picture (ideally a photograph) of how a lunar eclipse
> looks from the Moon (from there, it would be a solar eclipse).

I think the last camera on the moon itself was actually
with Lunochod 2 spending 5 months there in 1973, and the
images doesn't seem to be easily available (not sure if
they even had color).

So any photo would probably be taken from orbit by more
recent missions such as SMART-1, Kaguya or Chang'e-1. Being
solar powered and all that they may well have been in power
saving mode during lunar eclipes though ;)

By the way, googling for Lunochod, I arrived
at the following russian moon page:

   http://selena.sai.msu.ru/Home/Moon.htm

It contains an animation which looks distinctly POV-ish ;)

   http://selena.sai.msu.ru/Home/svechka.gif

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