Sketchup's sunset/sunrise times seem to differ from other sources

[dnrhead]

Hi,

I’m using Sketchup Make 2017 and noticed some weird behavior regarding the shadows.
I’ve set the Geolocation to Boulder, USA:

Then I set the Date & Time to 1/1/2021 to 7:27 AM.

If I activate shadows, no shadows are visible, because it’s night, if I increase the time by a minute, the shadows are shown.

So according to Sketchup, the sunrise time should be between 7:27 and 7:28 for January, 1st.
Also Sketchup::active_model.shadow_info["SunDirection"].z is negative at 7:27 AM and positive at 7:28 AM.

This differs from other services by about 5 minutes.

Every other service I tested says 7:23.
Also the sunset is postponed by the same time, so it’s not the difference between apparent sunrise/real sunrise.

Can somebody explain this difference?

Apparently I’m allowed to upload only one picture, so I combined the steps to reproduce here:

Best regards
Frank

[Anssi]

According to Wikipedia, there are four standard ways to measure sunrise time. The difference between them is in the league of four minutes.

[dnrhead]

Thank you for the answer, do you think it’s possible to get some insights about the implementation of the suns position and/or sunrise calculation (It seems that the sunrise calculation is just shadow_info[“SunDirection”].z = 0 solved for time)?