Celestia Forums

Is anyone working on a representation of the Ikeya-Zhang comet for Celestia? It'd be pretty cool to watch over the next couple of months... I'd try it myself, but I've only been using Celestia for 2 days, and the comet'll probably be gone by the time I got it working...

One of my major goals for Celestia 1.2.3 is good quality rendering of comet comas and tails. But right now, comets just look like asteroids, which you know if you've visited one of the only two comets in Celestia right now (Halley and Borrelly)

--Chris

Cool! Great news on the comet rendering, Chris. However, I was just after an orbital description of Ikeya-Zhang for the moment, so that I can use Celestia to help me find the damn thing
Anyway, I bit the bullet and decided to start hacking around for myself. I got the orbital elements from here: http://ssd.jpl.nasa.gov/data/ELEMENTS.COMET, and hacked about to create this file:

"Ikeya-Zhang" "Sol"
{
Texture "asteroid.jpg"

EllipticalOrbit
{
Period 366
SemiMajorAxis 51.2106127
Eccentricity 0.99009859
Inclination 28.12033
AscendingNode 93.37319
ArgOfPericenter 34.66594
MeanAnomaly 0.0215747
Epoch 20020318.97804
}

# These are all made up (copied from Halley)
Radius 7.5
RotationPeriod 170
Albedo 0.04
}

Only problem is, it just sits in the middle of the sun, and I've no idea why. Also, I'm pretty sure the Epoch is wrong. Anyway, I figured these were pretty standard problems/errors, so if anyone could help me out, that would be cool!

The problem is that Celestia doesn't deal well with orbits that have eccentricities very close to 1. Unfortunately, this includes a lot of comets. I'm trying to get Celestia 1.2.2 out today--I'll see if I can get a fix in before the release.

--Chris

Ok . . . I changed the orbital calculation so that orbits with eccentricities between 0.98 and 1.0 are handled correctly. There will probably be issues with eccentricities greater than about 0.999 and parabolic and hyperbolic orbits will certainly not work yet. But, I did get Ikeya-Zhang to appear in the correct place in the sky. One correction I had to make was to convert the epoch you listed to a Julian day number. Celestia doesn't accept epochs in the YYYYMMDD form right now.

--Chris