how do the time zones work in the us
In the continental United States there are four time zones (click here for a map): Eastern, Central, Mountain and Pacific. When it is noon in the Eastern time zone, it is 11 a.m. in the Central time zone, 10 a.m. in the Mountain time zone and 9 a.m. in the Pacific time zone. All time zones are measured from a starting point centered at England's Greenwich Observatory. This point is known as the Greenwich Meridian or the Prime Meridian. Time at the Greenwich Meridian is known as Greenwich Mean Time (GMT) or Universal Time. The Eastern time zone in the United States is designated as GMT minus five hours. When it is noon in the Eastern time zone, it is 5 p.m. at the Greenwich Observatory.