The correct answer is B) Altitude. In the horizon system of coordinates, the equivalent to latitude on the Earth is altitude. Altitude is the angular distance of a celestial body above the celestial horizon, measured in degrees. This is analogous to latitude, which is the angular distance of a point on the Earth's surface north or south of the equator, measured in degrees. The other options are incorrect because: A) Zenith distance is the angular distance of a celestial body from the zenith, not the horizon; C) Zenith is the point directly overhead, not a coordinate; and D) Declination is the angular distance of a celestial body north or south of the celestial equator, not the horizon.