What are the coordinates called that are used in the horizon system?

The coordinates used in the horizon system are referred to as altitude and azimuth. In this system, altitude measures the angle of an object above the horizon, with values ranging from 0 degrees (on the horizon) to 90 degrees (directly overhead). Azimuth, on the other hand, indicates the direction of the object from the observer's standpoint, measured in degrees clockwise from true north. This makes altitude and azimuth vital for navigating and locating celestial objects in the sky, particularly from a specific observation point.

The other terms listed refer to different coordinate systems. Declination and right ascension are used in the equatorial coordinate system, which is based on celestial coordinates akin to latitude and longitude used on Earth. Longitude and latitude pertain to geographic coordinates on Earth’s surface, while meridian and equator are references for measuring longitude and latitude, respectively. Thus, altitude and azimuth uniquely describe the position of celestial objects in relation to an observer's horizon.