How to (/request?..) get positionned in a particular alignem

[Rjp buisson]

I am newbe to Celestia
What a wonderful job they (you?) did! a pure marvel...
I intend to use this soft for education purpose with kids/adults here in France (high school & associations)
I seem to offer great capabilities for studying/understanding many astro phenomena in the geometry and dynamic domains!
I have so far a few questions to begin with:
1- how can I place the Observer on a peculiar line (alignement) defined by two choosen objects: say on Sun-Moon line, or Moon-Earth line forvexample (offering a suited point of view for eclipses analysis...)
1'- starting in such a position, how can easily
a- move on that line (1D move)
b- move within the plane orthonal to that line (2D move)
2- How can I place the Observer on a peculiar plane (alignement) defined by three choosen objects:(for ex Sun-Earth-Moon)
2' starting in such a position, how can easily
a- move within that plane (2D move)
a- move on a line orthonal to that plane (1D move)
and
...that's all for today and for my first question to you...
Jean Pierre

[don]

Howdy Jean Pierre,

Welcome to Celestia!

Do you want to do these things from the keyboard, or have you considered writing a script to do them?

There is a scripting forum here also (http://shatters.net/forum/viewforum.php?f=9), where scripting commands are discussed and folks post some of their scripts.

Celestia User's Guide: http://www.fsgregs.org/celestia/ (look for the file: Celestia User's Guide 1.3.1 - v.1.3.1C)

Preliminary Celestia .CEL Scripting Guide: http://www.donandcarla.com/Celestia/

Hopefully some of these links will help you find what you are looking for?

Once again, welcome Jean Pierre!

-Don G.

[Rjp buisson]

Howdy Jean Pierre,

Welcome to Celestia!
Do you want to do these things from the keyboard, or have you considered writing a script to do them?
Preliminary Celestia .CEL Scripting Guide: http://www.donandcarla.com/Celestia/
Hopefully some of these links will help you find what you are looking for?
Once again, welcome Jean Pierre!
-Don G.

Thanks alot Don for your kind anwser.
Yes my first demand and concern was a keyboard way to interact with Celestia, with respect to a particular alignement constraint (or coordinate system?)
But If I can't do it with my fingers (as it seems you say), I'll try to do it with my head and write some script orders :
In any case I'll go and visit the sites you mentionned and try to get familiar in writing scripts.
And later on, I'll come back with my (matured) questions

[Harry]

1- how can I place the Observer on a peculiar line (alignement) defined by two choosen objects: say on Sun-Moon line, or Moon-Earth line forvexample (offering a suited point of view for eclipses analysis...)
1'- starting in such a position, how can easily
a- move on that line (1D move)
b- move within the plane orthonal to that line (2D move)

What you are looking for is the "Lock" Coordinate Systems, which has its axis aligned with the line between two bodies. To select this coordinate system, choose the first body (say Earth) and press ":" to set it as you point of reference. Then select the next body (say Moon) and press "l". Now in the lower right corner there should be written "Lock Earth - Moon". Note: AFAICS you can't set it to "Lock Sol - Moon", only to "Lock Moon - Sol"...

But this does not solve the problem of setting the observer to the line between these two bodies. The best thing I can think of is to go to the Moon and then back to Earth and repeat if necessary. This gets you close enough. You can then move along that line simply be moving to or away from your reference body (press Home/End-key, use mousewheel, press both mousebuttons).

Now moving strictly orthogonal(?) to this line is much harder, and probably requires scripting...

2- How can I place the Observer on a peculiar plane (alignement) defined by three choosen objects:(for ex Sun-Earth-Moon)
2' starting in such a position, how can easily
a- move within that plane (2D move)
a- move on a line orthonal to that plane (1D move)
and
...that's all for today and for my first question to you...
Jean Pierre

Got no idea without resorting to scripting...

[don]

Thanks alot Don for your kind anwser. ... And later on, I'll come back with my (matured) questions

You are quite welcome.

No such thing as a "matured" question in my mind ... just plain "questions" that we all have.

In case you did not know yet, there is a file in the Celestia folder named "controls.txt" that lists the keyboard commands. You can also click the Help menu in Celestia, then Controls, to get a dialog box of keyboard controls. Lastly, one is also provided in the User's Guide. I suggested the User's Guide because it explains the use of most of the keyboard commands.

Looks like Harald got you going with the Lock command too.

Good luck and have fun!

-Don G.

[jim]

how can I place the Observer on a peculiar line (alignement) defined by two choosen objects: say on Sun-Moon line

Hi Jean,

A very nice task and I found a solution. You can combine any object with any other. For example I set the observer between Io and Europa close on Io's surface - very interesting if the time is accelerated. Or your Moon-Sun example realy nice to see a moon eclipse from this position (with a bit ambient light).

Before I start some general controls should be known:
- select an object
- adjust distance to selected object
- orbit(turn) the selected object

OK, what is to do for the Moon-Sun example?
The first step is to bring the observer on the line between Moon and Sun:
- Press 'space' to pause Celestia.
- Turn on labels for the wanted objects. In this case press 'M' and 'B' for Moon and star labels.
- goto Moon
- Now turn this as long as the Sun appears exact in behind the Moon (observer, Moon and Sun are on a line). I may usefull to use the zoom function(',' and '.'), increase distance to moon and turn orbits on for this job.
- To possition the observer between Moon and Sun select now the Sun (press 'H') then press 'F' to follow and reduce the distance to Sun a bit (press short 'Pos1' or use mouse weel).
-> The observer should be now exact on a line between Moon and Sun.

But I guess you want be close on Moon:
- press '*' to reverse the direction. The Moon should appear in the center. If it's to far away use the zoom function (',' and '.')
- select now Moon and press 'F' to follow
- set the distance to Moon you want
- press '*' to reverse the direction again to see the Sun
- The final step is to select Sun (you follow still Moon) and then press ':' (Shift + '.') to look the observer on the line between Moon and Sun.

That's all. Don't foreget to press 'space' again to start the animation. With 'J','K' and 'L' you can accelerate the time.

Bye Jens