Position and angle of Earth/Moon/Sun and timing

TouTorp

Hello all, I made an account here some time ago but hadn't got around to using it.

I'd quite like to build a program for getting the angle of the earth compared to vernal equniox (so I can convert from ECI to ECEF co-ordinates), angle of the moon relative to the earth, and angle of the sun relative to the earth.

There may be existing programs capable of doing so, but I'm intending to put this on a microcontroller, so are really going to be limited to doing this from scratch.

I think I'm going to be fine with the angle conversions and getting into different frames, but the issue is I don't know how to find out what the relative angles of these frames will be at different times. Say I want to know on September 18th 2013 at 20:00 GMT what the RA and DEC of the sun and moon will be, and I want to know what the angle of the earth will be compared to the celestial sphere, so I can get to what position they will be in the local sky at a given longitude and latitude.

Problem is, there are so many resources out there I really don't know where to start, been searching the past few days and still drawing a blank with what I need to be doing.

Any help would be much appreciated. Thanks!

Torpedo

Philosophaie

It is easiest to start in the Heliocentric frame then convert to the Geocentric Equatorial.

Nasa JPL has an Ephemeris that is helpful.

http://ssd.jpl.nasa.gov/?planet_pos