Hello all,

First of all, my best wishes to all of you. And to the developers of 
PovRay: keep up the good work; we're all grateful for the job you're doing.

My 5-year old son is very interested and intrigued by the interplay of 
the sun/earth/moon and how this creates day, night, seasons, ... Also 
the mechanism of a solar and lunar eclipse (who is casting a shadown on 
who) has caught his attention.

Since I lack a mechanical model of this three body system (I remember we 
had this in our geography classroom when I was in secondary school: you 
could turn a handle and then by means of gears the bodies would rotate 
and move), I was planning to do some animations with PovRay.

I don't want to re-invent the wheel, hence my question: is there anybody 
here who has done something similar with PovRay? I would like to end up 
with a small number of input files (or a single one) for which the clock 
variable would both make the bodies rotate and move the camera to show 
the different aspects (night/day, eclipse,...). 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?

Thanks for your tips!

bye,
gert

Post a reply to this message

You might want to try Celestia, a real-time planetarium program. 
Certainly, you can do the same things in POV-Ray, but there are several 
caveats:

1) POV-Ray is not a real-time program. You can't preview changes or 
interact with the scene in real-time. The best you can do is render 
individual frames to create a movie--which can be a time consuming 
process, and you'll have to start the process over from the beginning 
each time you make a mistake.
2) POV-Ray can suffer from floating point/rounding errors when the 
objects get too large and/or too distant.
3) POV-Ray takes a long time to master, in general; and creating scenes 
is usually a laborious process.

You could also try GeoGebra, which is a real-time dynamic geometry 
software. You could create representations of the planets as well as the 
shadows they cast on other bodies using geometric objects. This program 
is limited, however, to two dimensions.

Hope that helps.

-Mike

gvdeynde wrote:
> Hello all,
> 
> First of all, my best wishes to all of you. And to the developers of 
> PovRay: keep up the good work; we're all grateful for the job you're doing.
> 
> My 5-year old son is very interested and intrigued by the interplay of 
> the sun/earth/moon and how this creates day, night, seasons, ... Also 
> the mechanism of a solar and lunar eclipse (who is casting a shadown on 
> who) has caught his attention.
> 
> Since I lack a mechanical model of this three body system (I remember we 
> had this in our geography classroom when I was in secondary school: you 
> could turn a handle and then by means of gears the bodies would rotate 
> and move), I was planning to do some animations with PovRay.
> 
> I don't want to re-invent the wheel, hence my question: is there anybody 
> here who has done something similar with PovRay? I would like to end up 
> with a small number of input files (or a single one) for which the clock 
> variable would both make the bodies rotate and move the camera to show 
> the different aspects (night/day, eclipse,...). 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?
> 
> Thanks for your tips!
> 
> bye,
> gert
> 
>

Post a reply to this message

Hi Mike,

Thanks for the info. I've tried Celestia but thought it might be too 
complex for my son.

Concerning PovRay: I have some experience already (I'm playing with it 
since version 2 or so, have modeled our house in it, did some artwork 
for some websites I made, etc). So I think I can come up with something, 
I was just wondering if somebody already did something close to this and 
I could work further based on that...

I'll have a look at Geogebra...

thanks again,
gert

On 2009-01-06 14:33, SharkD wrote:
> You might want to try Celestia, a real-time planetarium program. 
> Certainly, you can do the same things in POV-Ray, but there are several 
> caveats:
> 
> 1) POV-Ray is not a real-time program. You can't preview changes or 
> interact with the scene in real-time. The best you can do is render 
> individual frames to create a movie--which can be a time consuming 
> process, and you'll have to start the process over from the beginning 
> each time you make a mistake.
> 2) POV-Ray can suffer from floating point/rounding errors when the 
> objects get too large and/or too distant.
> 3) POV-Ray takes a long time to master, in general; and creating scenes 
> is usually a laborious process.
> 
> You could also try GeoGebra, which is a real-time dynamic geometry 
> software. You could create representations of the planets as well as the 
> shadows they cast on other bodies using geometric objects. This program 
> is limited, however, to two dimensions.
> 
> Hope that helps.
> 
> -Mike
> 
> gvdeynde wrote:
>> Hello all,
>>
>> First of all, my best wishes to all of you. And to the developers of 
>> PovRay: keep up the good work; we're all grateful for the job you're 
>> doing.
>>
>> My 5-year old son is very interested and intrigued by the interplay of 
>> the sun/earth/moon and how this creates day, night, seasons, ... Also 
>> the mechanism of a solar and lunar eclipse (who is casting a shadown 
>> on who) has caught his attention.
>>
>> Since I lack a mechanical model of this three body system (I remember 
>> we had this in our geography classroom when I was in secondary school: 
>> you could turn a handle and then by means of gears the bodies would 
>> rotate and move), I was planning to do some animations with PovRay.
>>
>> I don't want to re-invent the wheel, hence my question: is there 
>> anybody here who has done something similar with PovRay? I would like 
>> to end up with a small number of input files (or a single one) for 
>> which the clock variable would both make the bodies rotate and move 
>> the camera to show the different aspects (night/day, eclipse,...). 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?
>>
>> Thanks for your tips!
>>
>> bye,
>> gert
>>
>>

Post a reply to this message

This may not help much, but here goes...

I wanted to do something similar but not for the Earth/Moon/Sun system. 
  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.

I wrote a simple model in POVRay and created an animation that captured 
one frame per hour for one year (143 Earth days) and clearly showed the 
geometry and timing of eclipses.

Notes:
	- as was mentioned, you have to be careful about scale
	- I didn't try modeling the elliptical nature of orbits - all orbits 
are simple circles
	- since I'm creating the world as a work of fiction, I have some  room 
to adjust the parameters to my suiting.

I can make this model available to you if you wish.  It could be 
adjusted to give an "impression" of the Earth/Moon system but couldn't 
be used to give accurate predictions of eclipses, etc.

David Buck

gvdeynde wrote:
> Hi Mike,
> 
> Thanks for the info. I've tried Celestia but thought it might be too 
> complex for my son.
> 
> Concerning PovRay: I have some experience already (I'm playing with it 
> since version 2 or so, have modeled our house in it, did some artwork 
> for some websites I made, etc). So I think I can come up with something, 
> I was just wondering if somebody already did something close to this and 
> I could work further based on that...
> 
> I'll have a look at Geogebra...
> 
> thanks again,
> gert
> 
> On 2009-01-06 14:33, SharkD wrote:
>> You might want to try Celestia, a real-time planetarium program. 
>> Certainly, you can do the same things in POV-Ray, but there are 
>> several caveats:
>>
>> 1) POV-Ray is not a real-time program. You can't preview changes or 
>> interact with the scene in real-time. The best you can do is render 
>> individual frames to create a movie--which can be a time consuming 
>> process, and you'll have to start the process over from the beginning 
>> each time you make a mistake.
>> 2) POV-Ray can suffer from floating point/rounding errors when the 
>> objects get too large and/or too distant.
>> 3) POV-Ray takes a long time to master, in general; and creating 
>> scenes is usually a laborious process.
>>
>> You could also try GeoGebra, which is a real-time dynamic geometry 
>> software. You could create representations of the planets as well as 
>> the shadows they cast on other bodies using geometric objects. This 
>> program is limited, however, to two dimensions.
>>
>> Hope that helps.
>>
>> -Mike
>>
>> gvdeynde wrote:
>>> Hello all,
>>>
>>> First of all, my best wishes to all of you. And to the developers of 
>>> PovRay: keep up the good work; we're all grateful for the job you're 
>>> doing.
>>>
>>> My 5-year old son is very interested and intrigued by the interplay 
>>> of the sun/earth/moon and how this creates day, night, seasons, ... 
>>> Also the mechanism of a solar and lunar eclipse (who is casting a 
>>> shadown on who) has caught his attention.
>>>
>>> Since I lack a mechanical model of this three body system (I remember 
>>> we had this in our geography classroom when I was in secondary 
>>> school: you could turn a handle and then by means of gears the bodies 
>>> would rotate and move), I was planning to do some animations with 
>>> PovRay.
>>>
>>> I don't want to re-invent the wheel, hence my question: is there 
>>> anybody here who has done something similar with PovRay? I would like 
>>> to end up with a small number of input files (or a single one) for 
>>> which the clock variable would both make the bodies rotate and move 
>>> the camera to show the different aspects (night/day, eclipse,...). 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?
>>>
>>> Thanks for your tips!
>>>
>>> bye,
>>> gert
>>>
>>>

Post a reply to this message

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?

Post a reply to this message

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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 ;)

- --
mailto:jeb### [at] freefr
http://jeberger.free.fr
Jabber: jeb### [at] jabberfr
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On Wed, 07 Jan 2009 09:51:15 +0100, gvdeynde <gvd### [at] gmailcom> wrote:

>I was just wondering if somebody already did something close to this and 
>I could work further based on that...


Hi Gert,
Out of interest I started to model an Earth Moon Sun system in a modeller and
quickly found that it not really easy to see what is happening when you use
proper scaling. For a five year old I assume that a non realistic model would
do.
Using a modeller you can show how the moon moves round the earth before
rendering. The modeller I used is Bishop3D and as it is in Beta it is free
http://www.bishop3d.com/ 
 
http://uk.youtube.com/watch?v=wsh6l7KpMEg

OK I know that the Earth should be moving but it is just a demonstration of a
shadow :)

-- 

Regards
     Stephen

Post a reply to this message

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?
> 
> 
> 

You need to have the two planets separated more than the Roche Limit 
otherwise the tidal forces will tear them apart.  In this case, they are 
about 10x the Roche Limit.  Within that range, it should be fine over 
long periods of time (billions of years) but I haven't done the 
simulations to verify that.

David Buck

Post a reply to this message

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.

A planet orbiting it's sun at a 20 lightyears radius would need to have an 
extra-galactic sun, or get snatched away by nearby stars. Such a planet would 
also be frozen solid, with, maybe, sone seas of liguid hydrogen and helium. It's 
"year" would last several 100's of millenias.


-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when your source files are starting to 
get bigger than the image files.
     -- Matt

Post a reply to this message

David Buck wrote:

> You need to have the two planets separated more than the Roche Limit 
> otherwise the tidal forces will tear them apart.  In this case, they are 
> about 10x the Roche Limit.  Within that range, it should be fine over 
> long periods of time (billions of years) but I haven't done the 
> simulations to verify that.
> 
> David Buck

Based on my undergraduate level physics education, I would say the other stability
limit is that the separation of the two planets should be substantially less than the
separation of the center of mass from the star.

Stability issues primarily occur with 3-body systems: they have a habit of ejecting
one of their members.  So as long as the system is a 2-body system, where one of these
bodies is itself a 2-body system, you're okay.

Dan

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