earth orbit accuracy

[gef]

Celestia was using the VSOP87 series that gave the Earth's position referred to the ecliptic and equinox of date. In 1.2.5pre7, I changed it to the VSOP87 series referred to the J2000.0 ecliptic and equinox (which is very close to the International Celestial Reference Frame). Which series to use is dependent on the application . . . I think xephem uses the equinox of date series. But in Celestia, since the positions of the Sun and other stars are fixed, the right choice is the series that uses a fixed equinox.

Thanks, I was looking for this last sentence
Although I did find in the CVS tree the apparent change in the reference
frame, I had found no comment on the judicium for doing so. Good.

An extra note:
The Xerxes' eclipse happened in October of *480BC* (-479), look at:
http://sunearth.gsfc.nasa.gov/eclipse/S ... story.html
This is to use for the homepage of celestia, where you announce v1.2.5

If only I could, make this run on ATI Rage Mobility M1
of this damned Acer Travelmate Laptop of me

cheers,
Fotis

[gef]

our (human race) eclipse predictions are fairly accurate,
because the near-earth celestial mechanics model
would be erroneous only if an event happened that gave energy to the
system of planets like earth-sun-moon (and the ones nearby, truly).

It requires excessive amount of energy in order to change
orbital elements like the period of a planet or even a satellite.

Note that, the earth spin slow down is caused by energy loss occured
due to friction of water molecules in the oceans. It's possible that there
are other such events that drive the system higher and higher in terms
of entropy, but their effects should not be greater than water friction.

(fun thought: how did earth's orbit change when that comet,
that is supposed to make dinosaurs to vanish, fall?
---insert your climate theory here---)

[dab]

hello again -- in case anyone is still interested in the fate
of old king Henry, I have found this site in the meantime:

http://www.phenomena.org.uk/CentralSolar.htm

they putatively identify `my' eclipse with the one of Aug 2nd, 1133
(so the chronicle entry would be 1.5 years off)

maybe next time I should do some research of my own first
But it was a very educating thread, thanks all!

dab