Latitude Maps

How do I calculate a simple angle from longitude and latitude?

I am trying to use ephemeris data for comet Halley to plot its orbit for use in Kepler's Laws. I need the angle from a horizontal that can easily be found with a protractor from Halley's longitude and latitude at different positions. I know this probably entails a sperical coordinate rotation, but I can't information on this. If you have a clue or even a site where I can find ephemeris that is easier to work with let me know A.S.A.P.

Public Comments

1. you tell us
2. Hope these are of use...
3. nobody knows
4. let's not forget that comets move in a sine wave, they do not travel in straight line, let's take in consideration magnitude and direction of the object...
5. Are these longitudes and latitudes heliocentric ecliptic coordinates ? By angle from the horizontal do you mean angle of the plane of the ecpliptic (essentially the plane of the solar system.) If so, than the latitude gives you that angle. They are one and the same.