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Cities on these meridians are Camden, New Jersey (Eastern), the western part of Memphis, Tennessee (Central), Denver, Colorado (Mountain), and Lake Tahoe, California (Pacific). For these cities, and other places on these meridians, local civil time, mean solar time, and standard time are all the same. |
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Following the publication of two papers by Sanford Fleming, an international conference was held in 1884 in Washington, D.C., with 26 nations represented. At the conference, it was agreed to establish a system of 24 international time zones around the world. Each zone is intended to represent 15 degrees of longitude (i.e., 2415 degrees = 360 degrees). At sea, the zone of any location is the mean time of the standard meridian running through the center of the zone. |
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Time zones are numbered consecutively from the Greenwich Meridian. Zones west of Greenwich are designated with a positive (+) number, and zones to the east are assigned a negative () number. The east coast of the United States, for example, lies 5 zones to the west of Greenwich, and lies in zone +5. The zone number is the negative of the actual number of hours of displacement, or offset, from GMT. Hence, zone +5 observes a time five hours earlier than GMT (5 hours). |
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Note that I use the older reference, GMT, and not the newer UTC (Universal Coordinated Time). The two designations are not technically equivalent but are close enough for the purposes of the discussion of time zones. |
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The original system relates time zones to displacement from GMT as shown in Table B.1. |
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B.4.2
Problems with the Time Zone System |
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Time zones are political, not scientific, matters. It is not surprising that the original simple system of 24 zones, although still extant in principle, has not survived in practice. Different countries are free to define local time zones that represent displacements from GMT not in integral numbers of hours. Thus, the original system of designation using a sign and an integer for each zone is inadequate to describe these zones. |
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The Washington conference of 1884 did not establish an international commission with jurisdiction of the zones. Since 1884, individual nations, in the absence of any international oversight, have redefined zone boundaries repeatedly, defined new zones, and even erected systems that are, in effect, attempts to bypass the entire system. As a consequence, the present system is a progressively failing patchwork, which combines the overall framework of the old 1884 agreement with a welter of supervening individual national definitions, conducted without international supervision. |
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A number of factors suggest that the present time zone system may not survive for many more years. First, the concept of a time zone introduces real errors in time keeping, simply for the expedience of certain industries in the late nineteenth century. Time zones are not better than local time. From the standpoint of accuracy, they are much worse. Time zones are certainly not modern, but relics of nineteenth century technology. Any application that requires correct time must introduce a correction for the error introduced by zone time. |
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