History of Time Zones

Before the adoption of four standard time zones for the continental United States, many towns and cities set their clocks to noon when the sun passed their local meridian, pre-corrected for the equation of time on the date of observation, to form local mean solar time. Noon occurred at different times but time differences between distant locations were barely noticeable prior to the 19th century because of long travel times and the lack of long-distance instant communications prior to the development of the telegraph.

The use of local solar time became increasingly awkward as railways and telecommunications improved. American railroads maintained many different time zones during the late 1800s. Each train station set its own clock making it difficult to coordinate train schedules and confusing passengers. Time calculation became a serious problem for people traveling by train (sometimes hundreds of miles in a day), according to the Library of Congress. Every city in the United States used a different time standard so there were more than 300 local sun times to choose from. 

Time zones were therefore a compromise, relaxing the complex geographic dependence while still allowing local time to be approximate with mean solar time. Railroad managers tried to address the problem by establishing 100 railroad time zones, but this was only a partial solution to the problem.

Weather service chief Cleveland Abbe introduced four standard time zones for his weather stations, an idea which he offered to the railroads. Operators of the new railroad lines needed a new time plan that would offer a uniform train schedule for departures and arrivals. Four standard time zones for the continental United States were introduced at noon on November 18, 1883, when the telegraph lines transmitted time signals to all major cities.

In October 1884, the International Meridian Conference at Washington DC adopted a proposal which stated that the prime meridian for longitude and timekeeping should be one that passes through the center of the transit instrument at the Greenwich Observatory in the United Kingdom (UK). The conference therefore established the Greenwich Meridian as the prime meridian and Greenwich Mean Time (GMT) as the world's time standard. The U.S. time-zone system grew from this, in which all zones referred back to GMT on the prime meridian.

At noon on November 18, 1884 the U.S. Naval Observatory sent out a telegraph signal marking 12:00 pm ET, and railway office in cities and towns across the country calibrated their clocks accordingly.

 However, it wasn’t until 1918 that standard time became the official law of the land, when Congress passed legislation recognizing the time zone system (and instituting a new “daylight savings time” designed to conserve resources for the World War I war effort).