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

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

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