# Thread: "hour angle" vs "azimuth angle"

1. ## "hour angle" vs "azimuth angle"

Hi all!

I am trying to describe the position of the sun depending on observer position, day of the year and hour. I am using the Duffie's and Beckman's book "Solar Engineering of Thermal Processes" as reference. But I have a problem to understand the difference between two angles appearing in the same equation: the "hour angle" (of the sun) and the "solar azimuth angle" (measured from the south).

Can anyone clarify me the definitions and the differences between these two angles?

I searched a lot and still not understood so, please, be very very clear...as I was (and maybe I really am) very stupid.

philooo

2. ## Re: "hour angle" vs "azimuth angle"

Welcome to the forum.

Hour angle is measured along the tilted great circle of the celestial equator. Azimuth angle is measured around the horizon. The motion around the hour angle circle is smooth, since it is just the rotation of the Earth. The motion around the horizon oscillates, speeding up and slowing down, depending on where the Sun is.

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4. ## Re: "hour angle" vs "azimuth angle"

Hi KeithBC!

So, if I have understood, the hour angle of the sun is linear in time, meanwhile the azimuth angle is sinusoidal. Am I right?

5. ## Re: "hour angle" vs "azimuth angle"

Originally Posted by philooo
Hi KeithBC!

So, if I have understood, the hour angle of the sun is linear in time, meanwhile the azimuth angle is sinusoidal. Am I right?
Correct.