Time Zones, are each of the 24 time zones drawn by an imaginary line from one pole to the other of the terrestrial globe.
The purpose of this division is to standardize the calculation of time across planet Earth. Before this methodology, clocks were set in each city that passed by or, as in the Middle Ages, by the apparent solar time at noon.

In the 1840s, Greenwich Mean Time was established with the center of the first time zone defined at the Royal Greenwich Observatory in England, located on the 0 degree longitude meridian.
The 24 time zones, each 15 degrees long (width) have a time zone equal to one hour, were set equidistant from each other, east and west of the Greenwich meridian. Today, when the time is 12:00 in Greenwich, it is 11:00 in the next time zone adjacent to the west and 13:00 in the next time zone adjacent to the east.

The time determined by the Greenwich Mean Time is called GMT. From this, the other time zone limits are established. The Earth makes its rotation movement by turning from west to east around its own axis, for this reason the spindles east of Greenwich (starting point) have the early hours (+); the spindles located to the west of the initial meridian have their hours delayed (-).