Stars are great. They are, essentially, fixed locations in 3D space relative to each other. What ChView calls planets are other objects which, instead of existing on their own, circle around another object, usually a star.
Like with stars, a bunch of basic data is already present embedded in the code. You can turn this on by setting the parameter DataType to "solsys". This gives you the planets of the Solar system.
<applet code=chview.ChViewer archive=chview.jar width=640 height=320> <param name="DataType" value="solsys"> </applet>
gives:
The name of the parameter is the same as for a star; i.e. "body001" up to "body999". Following the pattern you have been seeing, the value of this setting is a similarly cryptic line to that for a star. Here is an example:
<param name="body022" value="B!Sol Station!http://www.solstation.com/sol#earth!Earth!Terra!Sol!blue!1!365.24!0!4!0">
or, more abstractly:
<param name="body001" value="B!<comment>!<link>!<common name>!<stellar name>!<parent>!<color>!<orbital radius>!<period>!<tilt>!<radius>!<eccentricity>">
Lets look at each field.
This is always "B" for "body". (P probably would have been better for "planet" but there you go.)
These have the same function as they do with stars.
These also have the same function as they do with stars.
The difference between a star and a planet is that the planet goes around something. Here you need to name the object which the planet goes around. This is usually either a star or another planet. You can use either the common name or the stellar name.
If no parent is specified then the object is placed at 0,0,0 in the coordinate field.
Planets don't come in spectral categories like stars. So rather than categorize them by color, we let you give whatever color you wish. Values of this parameter are the same as used for mapping star colors.
As specified at the begining, we don't give a fixed 3D position to a planet. We give a parent whose position it is relative to. The three values Orbital Radius, Orbital Period, and Tilt are used to represent this position.
This is the distance that a planet is from the star. The units are arbitrary as you can modify them with the scale. Normally we would use AU, but if you are mixing stars and planets together in the same view, another unit may be more appropriate.
<applet code=chview.ChViewer archive=chview.jar width=640 height=320> <param name="body001" value="B!!!!Star!!yellow ! 0!0!0!4!0"> <param name="body002" value="B!!!One !!Star!darkgrey! 1!0!0!4!0"> <param name="body003" value="B!!!Two !!Star!green ! 2!0!0!4!0"> <param name="body004" value="B!!!Three!!Star!blue ! 3!0!0!4!0"> <param name="body005" value="B!!!Four !!Star!red ! 4!0!0!4!0"> </applet>
This is the time it takes a planet to go around its star. The units are arbitrary as you can modify them with the date control parameters. Normally we would use days, but another unit may be more appropriate depending on your application. If a value of zero is given, ChView works out an appropriate value depending on the orbital radius.
<applet code=chview.ChViewer archive=chview.jar width=640 height=320> <param name="body001" value="B!!!!Star!!yellow ! 0!0!0!4!0"> <param name="body002" value="B!!!One !!Star!darkgrey! 1!1!0!4!0"> <param name="body003" value="B!!!Two !!Star!green ! 2!2!0!4!0"> <param name="body004" value="B!!!Three!!Star!blue ! 3!4!0!4!0"> <param name="body005" value="B!!!Four !!Star!red ! 4!8!0!4!0"> </applet>
The tilt is how far the orbital radius is inclined to to the eliptic. That is a fancy way of saying how much of an angle it is compared to the other planets. The best way to see this is to turn it on its side.
<applet code=chview.ChViewer archive=chview.jar width=640 height=320> <param name="body001" value="B!!!!Star!!yellow ! 0!0!0!4!0"> <param name="body002" value="B!!!One !!Star!darkgrey! 1!0! 0!4!0"> <param name="body003" value="B!!!Two !!Star!green ! 2!0!10!4!0"> <param name="body004" value="B!!!Three!!Star!blue ! 3!0!20!4!0"> <param name="body005" value="B!!!Four !!Star!red ! 4!0!30!4!0"> <param name="theta" value="90"> <param name="phi" value="90"> </applet>
Again, because a planet has no spectral type we cannot classify its size either. So a parameter is given so that you can specify it on a planet by planet basis. The value of the parameter is in pixels as for Star Size.
Planets do not actualy orbit in circles. They orbit in elipses with the center of gravity of what they are orbiting being on of the focus points of the elipse. Eccentricity is used to describe how much flatter an elipse is from a circle. An elipse with an eccentricity of 0 is a circle. One with a value of just under 1 is a long, thin, flat, line. Values less than zero or greater than one are not allowed.
If you are working from real astronomical data you may find you have to exaggerate the eccentricity to make it visible to the naked eye.
You will also note that if you have the planets moving, that they will travel faster when they are nearer. This is the correct behaviour for planets. Trust me. The math is complicated, but it's done.
<applet code=chview.ChViewer archive=chview.jar width=640 height=320> <param name="body001" value="B!!!!Star!!yellow ! 0!0!0!4!0"> <param name="body002" value="B!!!One !!Star!darkgrey! 3!0!0!4!.0"> <param name="body003" value="B!!!Two !!Star!green ! 3!0!0!4!.2"> <param name="body004" value="B!!!Three!!Star!blue ! 3!0!0!4!.4"> <param name="body005" value="B!!!Four !!Star!red ! 3!0!0!4!.6"> </applet>
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