Jonathan Silverlight wrote:

In message , Jake
writes
Five replies to this thread and not one of them addressing the original
subject matter.

How sadly illustrative of what sci.astro has become.

In my case, it's because I was fairly sure Jim Green's reply had
absolutely nothing to do with the question, even though I was much less
sure what the questioner wanted ;-) It would be helpful to know why the
question is being asked.

Because I wanted to convert from celestial coordinates (aka equatorial
coordinates) to heliographic coordinates, which AFAIK are always
heliographic _ecliptic_ coordinates. I don't see the point of
heliographic equatorial coordinates, although such an oddity may exist
so maybe I should have been more specific.

This page has what looks like a useful description of doing the reverse
(converting heliocentric co-ordinates to right ascension/declination)
http://home.att.net/~srschmitt/script_planet_orbits.html
Here's another by Paul Schlyter
http://www.njsas.org/projects/tidal_forces/altaz/pausch/tutorial.html
I'm probably wrong, but it seems to me that converting from celestial
co-ordinates to heliocentric is about determining the orbit of an
object, which is a much bigger project.

Thanks, Jonathan.