Horizontal Coordinate System - Altitude & Azimuth

6.9 - Understand the use of the horizon coordinate system (altitude and azimuth)

6.10 - Understand how the observer’s latitude can be used to link the equatorial and horizon coordinates of an object for the observer’s meridian

These terms are based on the location of the observer at any given time. It is important to remember that over the course of long observing session the stars position will change.


We can measure how high in the sky an object is from any location on the horizon in degrees from 0° at the horizon to 90° at the zenith. An observer can find their latitude by the angle to the Northern Celestial Pole (NCP) marked by the star Polaris.
Altitude of NCP = Latitude of Observer


We can also measure its direction along the horizon. We take north as 0° and travel eastward increasing the angle until we reach 360° north again. An observer can fairly easily use this system if they have a reasonable grasp of estimating angles and know how to find north.

See the Celestial Calculations page to understand locations and timings of observing objects.



How high an object is above the horizon

How far an object is eastwards in degrees

Mix & Match

Explain the terms Altitude and Azimuth