Altitude and Azimuth
(Alt/Az) coordinates tell you where to look for an object in the
sky. These coordinates are taken from an observer's Latitude
and Longitude position.
The point in the sky
that's straight up over your head is called zenith. This point
has an Altitude of +90 degrees. The point straight down is
called nadir. It has an Altitude of -90 degrees. The
horizon has an Altitude of 0 degrees. If you look at an
object that's half way from the horizon to zenith, it would have an
Altitude of 45 degrees. Any Altitude coordinate that begins
with a minus is below the horizon and is not able to be seen.
Now you know that Altitude means how far up from the horizon to
Azimuth tells you which
direction to look. An Azimuth of 0 degrees tells you to look
north. An Azimuth of 90 degrees tells you to look east.
An Azimuth of 180 degrees tells you to look south. An Azimuth
of 270 degrees tells you to look west.
Now you can read Alt/Az
Example: If an object's
coordinates are at Altitude 30 degrees and Azimuth 190 degrees, you
would look a little west of due south, a third of the way from the
horizon to zenith.