What is the relationship between RA and Dec, and an objects visibility at a specific point on the Earth?

All angles are in radians:

Elevation angle.....e Azimuth angle.......A Geographic longitide.......glo Geographic latitude........gla Right Ascension............RA Declination................Dec Local Hour Angle...........HA

sin(e) = sin(Dec)sin(gla) + cos(Dec)cos(gla)cos(HA)

          sin(Dec) - sin(gla)sin(e)
cos(A) =  -------------------------
              cos(gla)cos(e)

HA = Local Sidereal Time - Right Ascension.

You will have to determine your Local Sidereal Time from the current Universal Time at your ground location, and the date of the observation.