Altitude and Azimuth: The Coordinates of the Sky You Actually See

Right ascension and declination describe the celestial sphere. Altitude and azimuth describe where an object appears from where you are standing.

Altitude is height above the horizon

Altitude measures angular distance above or below the observer’s horizon. An object on the horizon is near 0°; the zenith is +90°.

Sources: U.S. Naval Observatory — Computing Altitude and Azimuth

Azimuth is direction around the horizon

Azimuth measures direction along the horizon, usually clockwise from true north. Together, altitude and azimuth give an intuitive local position for a celestial object.

Sources: U.S. Naval Observatory — Computing Altitude and Azimuth

They change with observer and time

To convert from equatorial coordinates to local horizon coordinates, you need sidereal time plus the observer’s latitude and longitude. That is why a personal sky chart is genuinely geospatial.

Sources: U.S. Naval Observatory — Computing Altitude and Azimuth