Alternatively known as 'Alt/Az coordinates', this system of celestial coordinates is dependent on the observer's latitude and longitude. Using the observer's local horizon as a reference plane, the position of an object on the celestial sphere at a particular time is given by its:
The horizonal coordinate system depends on the location of the observer and the time of the observation. It measures the altitude
of an object in degrees to position it on the sky.
(alt) of an object can lie between 0o
(indicating it is on the horizon) and 90o
at the zenith
if it lies below the horizon). The azimuth
(az) changes from 0o
for an object due North to 90o
(due East) to 180o
(due South) to 270o
The horizontal coordinate system
is fixed to the Earth and not the stars
and therefore, unlike in the equatorial coordinate system
, the position of an object changes with time.