Google mash-up I'd like to see

On Dec 20, 8:55 am, Ilya Zakharevich <nospam-ab... DeleteThis @ilyaz.org> wrote:
> [A complimentary Cc of this posting was sent to
> David Bernier
> <david... DeleteThis @videotron.ca>], who wrote in article <T_kaj.6427$Bw2.501...@weber.videotron.net>:
>
> > Currently, effects from general relativity are included by JPL and
> > others. Trying to understand solar dynamics formulated
> > in general relativity is beyond me.
>
> I'm very sure that (maybe with an exception of Mercury; but I think
> even for it) the main term of the effects of GR can be expressed as
> minor additions to Newton inverse square law (a term of degree not
> -2, + a term depending on relative velocity). (I do not have a
> reference at hand, but I think it is in the beginning of any book on GR...)

I am pretty sure that the advance of the perihelion of mercury can be
accurately calculated from an eqn of motion that differs from the
Newtonian one only by a term (or 2) like the ones you describe. The
reason I'm so sure is that the last written exam I ever took was GR,
and that was one of the questions

Ilya Zakharevich <nospam-abuse RemoveThis @ilyaz.org> wrote:
> [A complimentary Cc of this posting was sent to
> David Bernier
> <david250 RemoveThis @videotron.ca>], who wrote in article <T_kaj.6427$Bw2.501387@weber.videotron.net>:
>> Currently, effects from general relativity are included by JPL and
>> others. Trying to understand solar dynamics formulated
>> in general relativity is beyond me.

> I'm very sure that (maybe with an exception of Mercury; but I think
> even for it) the main term of the effects of GR can be expressed as
> minor additions to Newton inverse square law (a term of degree not
> -2, + a term depending on relative velocity). (I do not have a
> reference at hand, but I think it is in the beginning of any book on GR...)

> Of course, this assumes the observer far away from the system, and not
> hopping from one body to another one. Which reminds me (an urban
> legend?):

> When first launched, GPS satellites had a (software) switch. In one
> position, they would take into account the effects of GR; in the
> other, they would not.

> Engineers being naturally suspicious of "high brow" calculations,
> the at-launch position was OFF. During the first day of testing,
> the errors accumulated so much, that they grudgingly agreed to turn
> it ON.

That's a geat story! I hope it's true!

I'm still very awed by the fact that only 250 years after Harrison
made a clockwork clock accurate enough to determine longitude for ship
navigation by means of time and celestial observations, you can now
buy for $200 a urban street satellite navigation device which times
its observations to 10 nanoseconds and requires relativistic time
corrections.

--
Chris Malcolm cam RemoveThis @infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/]