Solar Direction?

Hi,

I wanted to know if there are any algorithms which would allow one to
find the direction of a given place on the earth relative to one's own
position, using the Sun (and moon) as a reference.

e.g. I know that I am in London and that Paris is X degrees from the
Sun at a given time of day.

There would no doubt, be two separate algorithms. Abviously, if the
sun has set, values would not be possible. Same goes for the moon.

Anyone who can offer any help?

Many thanks,