Exercise:
From St.Andrews,
at 6 pm on 1998 February 2nd,
the Moon appeared at altitude +39°, azimuth 196°,
while Saturn is at altitude +34°, azimuth 210°.
How far apart did the two objects appear?
The difference in azimuth is 14°.
Use the cosine rule:
cos MS = cos MZ cos ZS + sin MZ sin ZS cos Z = 0.98
so MS = 12.3°
Which was further east?
The Moon is further east, and higher up, than Saturn.
Back to "the alt-az system".