I have been experimenting with the 'solpos' library from NREL, which is a very nice library for computing solar position (and related) calculations given date/time and coordinates.(adsbygoogle = window.adsbygoogle || []).push({});

One thing that surprised me is that the sun's rate-of-change in elevation (angle from the horizon) is not constant throughout the day. In fact, the elevation changes about 7-8 times faster at sunrise/sunset than it does at solar noon.

Here's sample calculations for Toronto Canada for January 19, 2009:

07:52:00: azim=118.788 elev=0.109222

07:59:00: azim=120.007 elev=1.209

...

12:28:00: azim=179.905 elev=25.9437

13:18:00: azim=192.848 elev=24.9487

I'm sure there's some perfectly good trigonometric reason why this should be the case, but at the moment I haven't been able to come up with a good explanation.

Can anyone help unravel this mystery?

Thanks,

Adam

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Why isn't the sun's rate-of-change in elevation constant?

**Physics Forums | Science Articles, Homework Help, Discussion**