Originally Posted by rickair7777

Time zones were created to account for the sun being at different elevations as you change longitude. Used to be that every town set their clock when the sun was high-noon, so the actual time in any location varied in random increments (100 miles away would be off by a few minutes). GMT (Zulu, Greenwich Mean Time) is the noon-based time in London, England and was selected as the universal "master" time. Greenwich (in London) is located on the prime (or zero) meridian. All other time zones are based on the that, but are offset by whole-hour increments to simplify conversion. But there's no reason you should have to know this on a commercial checkride.