I’ve ported some C code designed to calculate the suns position into javascript. It’s all part of my plan to make a clock that shows the local sunrise and sunset times on its face.
Given a bewildering number of parameters (most of which you can just guess), it will tell you the time of sunrise, sunset and solar noon.
It also has a few methods for calculating time based on fractions of days, and the Julian Day (a commonly used system in astronomy).
You can try it out here.