Art & Engineering

4. Global Positioning System (GPS) and the World Time Zones.

The satellite navigation system in the car is a matter of course today. The origins of the GPS date back to the middle of the 17th century. Without satellites with only a compass, sextants and chronometers, the ship's global positioning was carried out on the high seas. The degrees of longitude and latitude determine the precise position of a ship on the seas. Only the latitude could be determined in the 16th century with the help of the position of the sun or the stars. In the 17th century one believed that the degree of longitude could be determined via the distance to the moon. The moon, however, can only to a certain extent be located for navigation during the month.

For a simple solution of the longitude degree problem one needs the time as the fourth dimension. The earth turns once around its own axis in 24 hours or from the position of the sun in one hour by 15 degrees of longitude in west-east-direction (15 x 24 = 360). In case the precise local time can be determined with the position of the sun, for example 12 o'clock noon, so it is possible to define with a precision watch, whose 12 o'clock signalling is assigned to a specific meridian, for example the zero meridian in Greenwich, the time shift and with that the change of the degree of longitude to the reference meridian. The precision watch, a Chronometer, which describes the rotation of the earth synchronously, should run, even in rough seas, extremely precisely for months. A time deviation of one minute leads at the equator to a length error of 27.6 kilometres in west-east-direction and with that to considerable threats near shallows or dangerous reefs.

The time zones are derived from the time shift of the locally highest sun position round the world. Canada and the USA introduced for their countries the time zone system in 1883. In 1893 the Central European countries followed with the introduction of the "Central European time" (CET).

An exclusive classical time zone watch is the represented wristwatch with a mechanical calibre, fine adjustment and the integrated decentralized faces for two time zones. The local time is indicated on the right face and the time of any other time zone on the left hour face. Since minutes and seconds are identically in all time zones, the corresponding hands are

arranged centrally. The fascination and esteem of the clock lies in the timeless inner mechanics, a clock that will probably survive a digital wristwatch of today.