# Moon coordinates question

1. Aug 25, 2009

### Andru10

Hello, I am new to this forum and this is my first thread! :)

I would like to know how I can compute the Cartestian Coordinates (x,y,z) of the Moon, with the Earth at the origin during the eclipse of August 11 1999 at the time of the greatest eclipse point (http://en.wikipedia.org/wiki/Solar_eclipse_of_August_11,_1999). I'm trying to create a program that can predict Solar eclipses.
I have chosen the (x,y) plane to be the ecliptic plane (Earth-Sun plane), so the z coordinate of the Moon would have to be almost 0. I say almost 0 because, when I say coordinates, I'm referring to the coordinates of the center of the Moon ... and the center of the Moon, the center of the Earth and the center of the Sun weren't colinear during that eclipse (honestly I doubt there was an eclipse in which they were perfectly colinear). My program only works with points, not whole objects (not yet at least).

Thank you!

2. Aug 25, 2009

### mgb_phys

You might find them in your library - there are a few other books on astronomy coordinates but these are probably the easiest.

ps. you almost certainly don't want to work in XYZ but in earth centred ra-dec

3. Aug 25, 2009

### Ich

Last edited by a moderator: Apr 24, 2017
4. Aug 25, 2009

### tony873004

I find it easier to use Horizons email interface rather than the web interface, as you can create a template and use it over again with modifications. For example, sending the following email to horizons@ssd.jpl.nasa.gov, and putting the word job in the subject line gives you your desired data.
Horizons immediately mails you back an email that contains the following data. The numbers I boldfaced are your x,y,z positions, and x,y,z velocities.

5. Aug 25, 2009

### Andru10

Thank you all very much! This has been extremely helpful! :)