Mean Time

Our concepts of time are based on an earth centred (geocentric) view of the motion of the sun. 

Mean time (which is the time that our watches try and keep) is time based on the average (or mean) motion of a fictional sun which moves at a uniform rate.  

There are many related mean time measures. The most well known are Greenwich Mean Time and Universal Time.

The difference between Mean Time and True Time is called The Equation of Time.

Calculate it!

The Sun API's functions all work based on Universal Time.