Time Zones Explained

Time Zones – A Brief Guide

A time zone is a region with a standard time throughout that is used for all social, commercial and legal purposes within that region. The Earth is loosely divided into 24 regions (time zones) separated by longitude. Not counting local variations, each line of longitude is divided by fifteen degrees; as a general rule and depending upon which way one travels, time moves forward or backward one hour for every fifteen degrees of longitude.

Why Are Time Zones Used?

Before the late nineteenth century, most towns and cities across the world used to set their local times based on the observance of stars and the Sun. This was not an issue in and of itself at this time because, for the most part, the differences in time between long distances were barely noticeable due to the very long travel times taken to traverse these distances. As well as this, the lack of global (and even national) communications made the need for standard timekeeping irrelevant.

However, the latter part of the nineteenth century is well known for the explosion of global trading, and the expansion of communication and transport that inevitably came with this. The Industrial Revolution was in full swing, and the world was changing almost beyond recognition. Because of this, the need eventually arose for a better method of timekeeping. This gave birth to time zones, with the Greenwich Meridian becoming the first, or ‘Prime’, time zone in 1884.


How Do Time Zones Work?

As described above, in theory, each fifteen degrees of longitude moved toward the east corresponds to moving the clock an hour forward. In practice, however, this is a rather simplistic explanation, and things are not always as they seem. Time zone regions today, although roughly corresponding to fifteen degrees of longitude, conform more to national and international boundaries than to the rigid fifteen degrees longitude rule. 

The irregularity of the time zone borders is necessary politically and for the convenience of the local populace.


How Many Time Zones Are There?

This is pretty easy to work out with simple mathematics. There are 24 hours in a day, and 360 degrees of longitude encompassing the globe – dividing 360 by 24 gives you the 15 degrees of longitude that equates to a one-hour difference in each time zone. Based on this, you can then deduce that there are 24 time zones around the world.


Time Zones – a Historical Timeline

Believe it or not, time zones are historically linked to pendulum clocks. These clocks were initially developed in the seventeenth century, but it is what happened in the following century that interests us.

John Harrison, an English horologist, worked out that a clock could be used to precisely pinpoint a ship’s position at sea. This occurred in 1764 and, a year later, led to the now-famous Longitude Act, otherwise known at the time as the ‘Act 5 George III’. And because of their ability to measure time very precisely despite different conditions or speed/motion, chronometers became the instrument of choice for most mariners in the nineteenth century.

Despite this and the developments that had occurred with longitude, many cities and towns across the world still set their clocks based on sunrise and sunset.

In nineteenth century Unites States, for example, the fledgling American railroad maintained many, many different time zones across its route. Almost every station set its own time, meaning that nearly every city in the States was at different times from each other. This obviously caused huge issues for travelers, especially those that traveled long distances on the trains. All this chaos eventually led to the US adopting four time zones in 1883, by which time, though, Britain already had a standard system in place.

Britain played a leading role in garnering consensus for global time zones in 1884, which eventually led to the Greenwich Meridian being designated the Prime Meridian and Greenwich Mean Time as the world's time standard, leading to the eventual harmonisation of the lines of longitude and time zones.