Expanded it to work across an array of satellite tiles and added soft shadows. Softening shadows around the azimuth is easy because you just average samples (here, 16), and along the altitude is even easier because the horizon algorithm gives enough information to simply do a smooth fade.

A 24-hour loop of summer solstice sun rising over Mount Adams, Washington, USA. Not terribly user-friendly, but you can select a region and encode a loop here: observablehq.com/@rreusser/li...

I mean I sure thought so, but……

Alright, fixed the ad hoc lighting computation for my terrain shading, I think. Always tricky to balance good appearance and good controllability. Try it live here: observablehq.com/@rreusser/li...

The sun rising over Thor Peak, Auyuittuq National Park, Canada. It's using line sweep horizon tracking to compute ambient occlusion and physically accurate shadows together with relief shading, all packed into an RGBA texture. Pretty happy with the scanline algorithm, but the shading needs work.

Nice! And the antialiasing is a good idea which had been bugging me. I'd be curious to know how you approached it. My approach was to use quasirandom noise to jitter the points (because it's fast, very easy to implement in a shader, and good enough).