What is the difference between azimuth angle and hour angle?
Azimuth is measured along the local horizon: 0° is geographic north, 90° is east, and so on.
Lines of equal azimuth converge at the zenith and nadir.
Hour angle is measured along the celestial equator: 0h is the local meridian, 6h is in the western sky, etc.
Lines of equal hour angle converge at the celestial poles.
In other words, the two angles are measured around different axes.
The angle between those axes is the complement of the observer's latitude.