#175 Eclipse Finder doesn't work with JPL ephemerides

v1.5
closed-rejected
Chris Laurel
5
2008-01-25
2008-01-22
Ulrich Dickmann
No

The Eclispe Finder doesn't work (at least for Earth
and Moon) when JPL ephemerides (DE406 -> jpleph.dat)
is enabled by a modifying .ssc like

...

Modify "Earth" "Sol"
{
CustomOrbit "jpl-earth-sun"
}

Modify "Moon" "Sol/Earth"
{
CustomOrbit "jpl-moon-earth"
}

...

=> The calculations are wrong.

Discussion

  • Chris Laurel
    Chris Laurel
    2008-01-24

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    Originator: NO

    I'm quite sure now that this is not a bug, though there is an oversight in the documentation on the WikiBook. All of the JPL orbits are in J2000 ecliptical coordinates. This is the default reference frame for planets in Celestia. Unfortunately, the default reference frame for moons is different: the reference plane is the equator of date for the planet that the moon orbits. To accurately place the moon using the JPL ephemerides, you need to override the default orbit frame for the moon:

    OrbitFrame { EclipticJ2000 { Center "Sol/Earth" } }

    The WikiBook should be updated with a note about the reference frame for JPL ephemeris orbits. (The native reference plane for the JPL ephemerides is the Earth equator of J2000.0--they are rotated to the ecliptic reference frame by Celestia so that the default VSOP87 orbits can be easily replaced.)

     
  • Logged In: YES
    user_id=1719950
    Originator: YES

    Yep. That helps.
    Thanks.

     
  • Chris Laurel
    Chris Laurel
    2008-01-25

    Logged In: YES
    user_id=159994
    Originator: NO

    Closing this tracker item. The WikiBook was updated, but no code change required.

     
  • Chris Laurel
    Chris Laurel
    2008-01-25

    • status: open --> closed-rejected