Moon rotation/revolution fictional modification

[ANDREA]

Sorry for this topic, that I'm writing after many useless tryes.
This is my problem: I'm writing a cel script regarding the Moon (Earth's), and in order to give a clear "Celestia" evidence of the reason why the Moon rotates once for every orbit around Earth, I wished to use an Earth-Moon fictional system, similar to the one I use in my "The Orrery" add-on.
So I put Earth in Jupiter's position, with the Moon very close, about 3-4 Earth radii.
My problem is that with this configuration I'm unable to obtain the Moon showing always the same side to the Earth.
Any help, please? I tried many different solutions, without results.
Perhaps it cannot be done anyway, because out of phisics laws?
Thanks a lot for your time.
Bye

Andrea

[selden]

Are you using the Moon's CustomOrbit, or are you doing it with an EllipticalOrbit ?

It would help to see the SSC file that you're using.

[selden]

Here's a simple example using circular orbits.
Celestia automatically draws solar system bodies tidally locked if you don't specify any RotationPeriod or orientation information.

I copied the orbit information from Jupiter and Io.

Code: Select all

"Earth2" "Sol" {

   Radius 100000
   Texture "earth.*"

   EllipticalOrbit {
   Period           11.8622
   SemiMajorAxis     5.2034
   }
}

"Moon2" "Sol/Earth2" {
   Radius 50000
   Texture "moon.*"

   EllipticalOrbit {
      Period         1.769138
      SemiMajorAxis  421600
   }
}

[ANDREA]

Are you using the Moon's CustomOrbit, or are you doing it with an EllipticalOrbit ? It would help to see the SSC file that you're using.

Hello Selden, you are a rocket, indeed!
You are right, I forgot to give this info, so here is the ssc file I'm using for the fictional couple Earth-Moon:

"Jupiter" "Sol"
{
Texture "earth.*"
NightTexture "earthnight.*"
# SpecularTexture "earth-spec.*"
Color [ 0.85 0.85 1.0 ]
SpecularColor [ 0.5 0.5 0.55 ]
SpecularPower 25.0
HazeColor [ 1 1 1 ]
HazeDensity 0.3
Radius 3000.00 # equatorial
# Oblateness 0.0034

# BumpMap "earthbump.*"
# BumpHeight 4.5

Atmosphere {
Height 60
Lower [ 0.43 0.52 0.65 ]
Upper [ 0.26 0.47 0.84 ]
Sky [ 0.40 0.6 1.0 ]
Sunset [ 1.0 0.6 0.2 ]
# Sunset [ 0.3 1.0 0.5 ]
CloudHeight 7
CloudSpeed 0
CloudMap "New-Northern-Summer-Clouds_8kDDS.dds"
#CloudMap "New-Northern-Summer-Clouds_8kDDS copy.dds"
#CloudMap "New-Northern-Summer-Clouds_8kDDS.png"
#CloudMap "New-Northern-Summer-Clouds_8kDDS-JPG3.jpg"
}

#CustomOrbit "vsop87-earth"
EllipticalOrbit {
Period 11.0000
SemiMajorAxis 11.0000
Eccentricity 0.0167
Inclination 0.0001
AscendingNode 348.739
LongOfPericenter 102.947
MeanLongitude 100.464
}

RotationPeriod 23.9344694 # 23.93419
Obliquity -23.45
RotationOffset 280.5 # offset at default epoch J2000

Albedo 0.30
}

"Io" "Sol/Jupiter"
{
Texture "moon.jpg"
#BumpMap "moon-bump map-2k.jpg"
BumpHeight 0.1
Radius 825
# Oblateness 0.002

# CustomOrbit "moon"
EllipticalOrbit {
Period 27.321661
SemiMajorAxis 9000.0
Eccentricity 0.054900
Inclination 5.15 #WAS 5.15
}

Obliquity 23.45 # mean axis
EquatorAscendingNode 0.0 # mean axis
RotationOffset 38

Albedo 0.12
}

I'm using an Elliptical Orbit, but I'm sure I'm making a mistake, but I'm unable to find it.
Thanks a lot for your reply.
Bye

Andrea

[selden]

I think you're just making it way too complicated.

Try my simple example above and add only what you really need.

[ANDREA]

I think you're just making it way too complicated.
Try my simple example above and add only what you really need.

You are right, as usual, Selden. The problem of my making it too complicated, is that I completely missed the information (wherever it is!) regarding the auto-drawing of solar system bodies tidally locked, when not specifying any RotationPeriod or orientation information.
This made my life complicated, while the solution you gave me is so simple and immediately working.
Alas, my ignorance defeated me again.
Selsen, my students will surely agree if I say "Thank you, Selden" for them too.
Bye

Andrea

[selden]

Andrea,

You're very welcome, of course!

[rra]

Andrea, if it works what you try to show,
could you post your CEL -script to us (or me) .
I would like to visualize the cause of an solar-eclipse on earth,
most of the simple visualisations give a solar-eclipse every month,
which clearly isn't the case.
Bye the way: what does this "tidal lock" mean ??

Ren?©

[selden]

"tidal lock" means that the body has one face always toward the object it's orbiting around. It's called "tidal" because it's a result of the tides caused by the body it's orbiting around, stretching it out of shape and pulling harder on the part that's closest. Rather than go into all the details, I suggest you look it up.

[Johaen]

http://en.wikipedia.org/wiki/Tidal_lock

I <3 Wikipedia!

[ANDREA]

Andrea, if it works what you try to show,
could you post your CEL -script to us (or me) .
I would like to visualize the cause of an solar-eclipse on earth,
most of the simple visualisations give a solar-eclipse every month,
which clearly isn't the case.
Bye the way: what does this "tidal lock" mean ??
Ren?©

Ren??, I'll be pleased to post you my script, but when it will be finished, obviously.
Actually I'm working on Moon "Phases", but I think I'll need one more week before it will be ready.
I'll inform you.
Bye

Andrea

[rra]

Can't wait to see this.

In the mean time I tried your orrery but can't get the thing to work
(with 141 that is , I see no orbits at all),
what should I do when I want to use the orrery in the 1.4.1. Celestia version ??

Ren?©

[ANDREA]

Can't wait to see this. In the mean time I tried your orrery but can't get the thing to work
(with 141 that is , I see no orbits at all),
what should I do when I want to use the orrery in the 1.4.1. Celestia version ?? Ren?©

Ren??, actually I have The Orrery on a new 1.4.1 installation, and it works very well.
Try this: install 1.4.1, and substitute its files with the corresponding Orrery files, in the respective subdirectories.
Give a try and inform me on results.
Bye soon

Andrea