[Celestia-developers] Galilean Orbits Bug Fix

[Fridger S. <t0...@ma...>]

I have just checked in a  small but crucial bug fix (customorbit.cpp) that
raises the accuracy of the Galilean Jupiter moon orbits to spectacular levels
(see my thread in the Forum):

After systematically comparing the predictions for the Galilean moons
from Chris' checkin yesterday,  with Jean Meeus mutual event listing in
Dec. 2002 S&T, p. 100 ff, it was soon clear to me that something in
the 'customorbit.cpp' code for the /latitude/ calculation of the four
Galilean Jupiter moons was fishy. Soon I found it:

// Calculate periodic terms for the tangent of the latitude
....
B = degToRad(B);
B = atan(B); 

Indeed it's tan(latitude) that is computed in ... and hence the
statement B = degToRad(B); makes no sense and is actually incorrect.

After commenting B = degToRad(B); out for all four Galilean moons, the
resulting predictions turn out to be /spectacularly accurate/ without
any fiddeling whatsoever!! Everything with Chris'/Grant's parameters.

Here are just two amazing examples, but I have explicitly and
successfully tested most of J. Meeus event listings!:

1) The /annular/ eclipse shadow of Europa on Io (2e1A) on Dec. 

http://www.shatters.net/~t00fri/images/2e1A.jpg

2) The /total/ occultation of Europa by Callisto (4o2T) on Dec. 15

http://www.shatters.net/~t00fri/images/4o2T.jpg

Bye Fridger