The sun, on any day, is at its highest point in the sky at noon; at the equinoxes (roughly March 21 and September 22), the sun rises at 6 AM, Apparent Time, reaches its highest point at noon, and sets at 6 PM. Clock Time can be very different: for example, during the summer Britain (in common with many other countries around the world) shifts its clocks forward by one hour - so-called Daylight Saving Hours - so the sun will be at its highest at 1 PM, Clock Time. As another example, Iceland by choice sets its clocks to GMT, but Reykjavik is a full 22� west of Greenwich - so the sun rises on the equinox at 6:00 AM, Apparent Time, or at 7:28 AM, Clock Time (in other words, it takes one hour and twenty-eight minutes for the earth to rotate to the point where the sun's rays are highest in the sky over Reykjavik). Based on theoretical standard time zones of 15� width and being based on a central meridian that is some multiple of 15� from the Prime Meridian, Iceland's time zone should should extend from 22.5� W to 7.5� W and it should be one hour behind Greenwich Mean Time (now officially called Universal Coordinated Time). Source: http://www.locationworks.com/sunrise/tutor.html