solarsys.scc values....

[rbroberts]

I'm not sure if this question belongs in scripting, but since that's what I was trying to do when I ran into the question....

I was sitting down to calculate positions for a trajectory based on the solarsystem_tour script (which is basically calculate every position "by hand" in the script). The trajectory I want is a looping tour above and below the ecliptic where I cross the ecliptic on a line from the stop through the ascending/descending nodes of each of the planets in order to display the (small) non-planar nature of the orbits.

I figured solarsys.ssc was the quickest way to get the data I needed to do the calculation. But when I looked at the Earth data to make sure I was seeing what I expected, I became confused.

The inclination of earth's orbit is listed as 0.001 and the acending node is listed as 348.739. I thought the inclination should be zero. When I referenced Meeus (Astronomical Algorithms, 1998), he puts it a zero whether using J2000 or EOD. And the ascending node is (naturally) not listed for EOD but set at 174.873 for J2000.

But the values Celestia has for Venus are (almost) identical to Meeus. Can someone point me to an explanation on the differences?

TIA,

roland

[chris]

I'm not sure if this question belongs in scripting, but since that's what I was trying to do when I ran into the question....

I was sitting down to calculate positions for a trajectory based on the solarsystem_tour script (which is basically calculate every position "by hand" in the script). The trajectory I want is a looping tour above and below the ecliptic where I cross the ecliptic on a line from the stop through the ascending/descending nodes of each of the planets in order to display the (small) non-planar nature of the orbits.

I figured solarsys.ssc was the quickest way to get the data I needed to do the calculation. But when I looked at the Earth data to make sure I was seeing what I expected, I became confused.

The inclination of earth's orbit is listed as 0.001 and the acending node is listed as 348.739. I thought the inclination should be zero. When I referenced Meeus (Astronomical Algorithms, 1998), he puts it a zero whether using J2000 or EOD. And the ascending node is (naturally) not listed for EOD but set at 174.873 for J2000.

But the values Celestia has for Venus are (almost) identical to Meeus. Can someone point me to an explanation on the differences?

TIA,

roland

I wouldn't pay too much attention to the elements for the Earth's orbit in solarsys.ssc. Those are overridden by the VSOP87 CustomOrbit and are thus never used. I've left them in for reference, but a good case could be made for their removal. At the very least, there should be a comment pointing out that the Keplerian elements aren't used.

I'm not sure where those Earth's elements in solarsys.ssc originated. They're supposed to be the mean orbital elements, but perhaps they're osculating elements instead?

--Chris