Each of the 24 parties that is arbitrarily divided the earth's surface, to define and unify the country's legal time is called time zone. The spindles used as reference the Greenwich meridian. Each spindle has a central meridian and each of them is separated from the next by a length of 15 degrees. In any area of each zone, the time for the local time of central meridian, which is obtained by adding or removing at the time of Greenwich Mean Time (Universal Time) a number of hours depends on the spindle. For example, when the 12 in Greenwich are 13 in Italy, which is located in the contiguous zone, while in Chile are the seven, since this country is five time zones west of Greenwich, and therefore subtracted the number of hours.
In several countries tried to unify the official time for the entire territory, although according to time zones have differences in some of their areas. In these cases, the limits of the deformed zones, which, on the other hand, are arbitrary.
Yes. If the territory of a state is very long from east to west may have several official hours. For example, Brazil has two official hours, while Russia has eleven, and Canada and the United States, four.