Solar Position
The position of the Sun in the sky varies continually throughout the day and also changes signficantly over the course of a year. It is also very location-dependant, so it is critical that you know the latitude and longitude of your development site before you begin any calculations. Despite our fundamental physical understanding of solar position as a result of experiencing it every day, calculating it at any specific date and time is by no means a trivial exercise. The tilted rotation of the Earth and its elliptical orbit around the Sun add significant complexity to the equations required. Add the fact that one day isn't actually the time required for a full rotation of the Earth around its axis and that 365 days isn't actually the time required for a full orbit around the Sun, and we're in for some real fun and games.