Halley's Comet XYZ - 261 BCE to 2380 CE

[chrisobyrne]

After a prodigious amount of calculation I am pleased to announce the availability of an XYZ file for Halley's comet. You can pick it up at http://www.chris.obyrne.com/celestia/. This file runs from 261 BCE to 2380 CE. Whereas the results for ancient apparitions of this comet are as good as I can make them, they may not represent what our forebearers saw with great accuracy!

This XYZ file is the result of three numerical integrations that I did that produces results that don't quite agree with the (numerous!) scientific papers on the motions of this comet - and, of course, those papers don't quite agree with each other either! However, for near-recent times, the results should be quite good, and they should be "respectable" for ancient times, given that it seems that the true position of this comet isn't too well known for those times.

Also, I'm not sure how to install the xyz file so that it over-rides the built-in Halley's comet in Celestia (or maybe that's just a Halley's comet that I downloaded somewhere!). If someone could tell me how to do it properly, my email address is listed on the web page above.

[Evil Dr Ganymede]

I dunno if I'm looking at the right thing here, but when I go back to March 26th 1066 (which is the perihelion of Halley as recorded on the Bayeux Tapestry), it's at 27.211 AU from Earth. So that can't be right. I don't think that's your version though.

I think you need to provide a new SSC file for Halley that looks kinda like the ones for the spacecraft that have xyz files (like the one shown below) - I don't think providing the xyz on its own replaces anything:

Code: Select all

"Galileo" "Sol"
{
   Class "spacecraft"
   Mesh "galileo.3ds"
   Radius   0.01

   InfoURL "http://galileo.jpl.nasa.gov"

   Beginning "1989 10 19 02:47"   # Launch
   Ending    "2003  9 21 10:44"   # Crash into Jupiter

   SampledOrbit "galileo.xyz"
   EllipticalOrbit
   {
   Period        64.4068
   SemiMajorAxis  4632880
   Eccentricity   0.831774
   Inclination    4.213
   AscendingNode  59.562
   ArgOfPericenter 97.224
   TrueAnomaly    -66.619
   }

   RotationPeriod    1.0e9  # Essentially no rotation . . .
   Orientation     [ 90 0 1 0 ]

   Albedo         0.50
}


(as an aside, I can't set the time manually to that date. The year is out of the acceptable input range, it seems).

[chrisobyrne]

I dunno if I'm looking at the right thing here, but when I go back to March 26th 1066 (which is the perihelion of Halley as recorded on the Bayeux Tapestry), it's at 27.211 AU from Earth. So that can't be right. I don't think that's your version though.

I don't think Celestia is picking up the XYZ file correctly. I now have two comet Halleys on my Celestia - one of them is 27AU from the Sun in 1066, the other is at perihelion where it should be!

(as an aside, I can't set the time manually to that date. The year is out of the acceptable input range, it seems).

I think I remember something in the FAQ or other documentation about that - apparently, it's a bug in Windows, and doesn't happen for anyone who uses a "real" operating system.

[chrisobyrne]

The way I installed the XYZ file was by placing it in Celestia's data directory, and by creating a halley.ssc file in the extras directory -

Code: Select all

"1P Halley" "Sol" # the / causes "Select" problems in Celestia
{
Class "comet"
Texture "asteroid.jpg"
Mesh "asteroid.cms"
Radius 1.3          # km
RotationPeriod 6.23 # hours

SampledOrbit "halley.xyz"

EllipticalOrbit
 {
 Period               74.69609   #years for Solar objects
 PericenterDistance    0.592782247 #Astronomical Units
 Eccentricity          0.966577772 #pure number
 Inclination         161.9650996   #degrees
 AscendingNode       59.3924215   #degrees
 ArgOfPericenter     112.0521911  #degrees
 MeanAnomaly              0.0   #degrees travelled along the orbit
                                # since pericenter passage
 Epoch              2474034.2193883 #2061 Jul 28.7193883 Julian equivalent
                                # date of pericenter passage
 }
}


Happy hunting!

[selden]

Please read the thread http://www.shatters.net/forum/viewtopic.php?p=39890&highlight=replace+modify+add#39890

If you're running Celestia v1.3.2 or later, you can replace the definitions of any of Celestia's predefined objects by your own without actually editing any of the files that come with Celestia.

If you create a directory in \extras\ specifically for your own Addon, within it you can create a \data\ subdirectory containing your Addon's XYZ file and Celestia will find it.