# Get time from sun Azimuth

I want to know if I can determine the time where the sun's azimuth is at a given value.

In other words, I want a function that takes the sun azimuth along with longitude or time zone and outputs the time. Is there anything like this?

• A sundial? 8-)} – Keith Thompson Oct 16 '11 at 21:24

The sun moves one degree in 15 minutes, so for every degree east of south the time is 15 minutes before midday. For every degree past south it is 15 minutes after midday.

Though this is modulated by the Equation of Time for which you will need to refer to tables such as those published in the NOAA Almanac.

To expand; You can subtract your longitude from the suns azimuth, then multiply this by 15 minutes:

time = $[\theta_{sun} - \theta_{long} ]\times 15 \rm{mins} + \rm{EoT correction} + 12 \rm{Hours}$

so at $\theta_{sun} = \theta_{long}$ it is midday, for $\theta_{sun} < \theta_{long}$ it is morning and for $\theta_{sun} > \theta_{long}$ it is afternoon.

• Thanks for the answer, but can you explain more how to calculate this ? – Mina Samy Oct 16 '11 at 11:05
• Hi Nic, what is the result of this equation, is it in hours or minutes ? – Mina Samy Oct 18 '11 at 14:12
• sorry, its a bit sloppy, but the 15 mins implies theta is in degrees. The resultant units is up to you, just change the 12 hours to minutes or the 15 minutes to hours... – Nic Oct 18 '11 at 15:29