I need help

[Eyes of the Night]

I have Celestia. And I want to modify or create the solar system.

I don?t know the steps to do it.

If you want, help me.

thanks!

[billybob884]

it really isnt that hard contrary to my earlier beliefs:
(change all the bold text

"planet name" "star name"
{
Texture "whatever.wht"
Radius 1234
Atmosphere {
Height (earth is 60)
Lower [ 0.0 1.15 1.5 ] (this is the color of the atmosphere devided into 3 parts in RBG order, 1.15 is 115)
Upper [ 0.0 1.15 1.5 ] (same)
Sky [ 0.0 1.15 1.5 ] (same)
CloudHeight (earth is 7)
CloudSpeed (earth is 65)
CloudMap "cloudtexture.wht"
}

EllipticalOrbit {
Period (time it takes to revolve around an object in days)
SemiMajorAxis (distance from the center of itself to the center of the object it revolves around)
Eccentricity (offset it gets closer or further from an object)
Inclination (degrees orbit is tilted upward)
AscendingNode (longitude of the intersection point of the orbital plane (node line) with the equatorial plane)
ArgOfPericenter (longitude of the perigee with respect to the line of node)
LongOfPericenter (um... not sure)
MeanLongitude (um... not sure)
MeanAnomaly (position of the object in its orbit (from 0 to 360 degree with respect to perigee))
}

RotationPeriod (period of rotation on its axis in hours)
Obliquity (degrees an object's axis is tilted)
Albedo (brightness of the object from a distance)
}

moons are pretty much the same, but instead of

"planet name" "star name"

it looks like

"moon name" "star name/planet name"

[billybob884]

now, does anyone know how to make a comet? (mainly one with a tail)

[selden]

Mike,

To specify a comet, you have to be running some variant of Celestia v1.2.5. You then just include the line
Object "comet"
in the body of its .ssc file. Other options are Object "moon" or Object "spacecraft" or Object "asteroid" or Object "planet".
If you don't specify the Object "type", Celestia guesses based on its size. "comet" happens not to be in its list of things to guess.

Alternatively, you could design an arbitrary 3ds file...

A purist would have some quibbles with some of your definitions for ssc parameters(especially SemiMajorAxis) but they're close enough for starters. For the visually oriented, I made a crude diagram of the parameters at http://www.lns.cornell.edu/~seb/celestia/orbital-parameters.html I've gotta clean up the picture some.

[billybob884]

thanks for the comet help! well, i've gathered these thanks to other forum members, so if you got beef wit me, you got beef wit them! just kidding. but seriously, any corrections for really wrong ones will be appricated!

[billybob884]

a few more questions, how do you specify the comet's tails' length?, can you change the comets color?, and can you use more than one color in a tail, like blending them like a real comet? thanks

[selden]

MIke,

The distinctions between what you wrote and the precise definitions are subtle.

Period: right

The SemiMajorAxis is half the length of the long dimension of an ellipse. For a circle, what you wrote would be correct.

The Eccentricity is a measure of how elongated the ellipse is. I'm being vague ("a measure") It's 0 for a circle, >1 for a hyperbola (open at one end).

Inclination: right
Ascending Node: right (as far as it goes -- there's some more to the definitoin)

ArgOfPericenter: short for "the Argument of the Pericenter": the number of degrees that the pericenter is from the Ascending Node, measured in the plane of the object's *orbit*. Nobody knows why it's called "Argument". Apparently it's been called that since at least the 1300s.

LongOfPericenter: short for "the Longitude of the Pericenter: -- The sum of the Longitude of the Ascending Node and the Argument of the Pericenter. It's sometimes called a "broken angle", since it involves measurements in both reference and orbital planes.

Mean longitude: the sum of the Maan Anomaly and the Longitude of the Pericenter. It's another "broken angle". It's the angular distance in the reference plane from the 0 point of Longitude to the Ascending Node, and then the number of degrees in the plane of the orbit from the Ascending Node to the Pericenter, plus the number of degrees from there around the orbit to the orbiting object itself.

Mean Anomaly: right. So are the rest.

Whew.
I hope this helps a little.

[selden]

Mike,

Sorry:

The way they're defined right now the only thing you can control is the size of the comet. It's proportional to the radius of the object that forms its nucleus.

There's no way to specify the color in the current version. They're just shades of blue.

They seem to look brighter if you define more than of them at the same coordinates, though.

[billybob884]

thanks!