Time Zone Information

Standard Time Zones

People who are keeping time may be most familiar with Greenwich Mean Time (GMT). Greenwich Mean Time is based on solar time, and this is influenced by the Earth`s rotation. Since this is not constant, it is not the most reliable method of keeping track of time.

Because the time kept changing, atomic clocks (which use an atomic resonance frequency standard as a timekeeping element) needed to be changed in order to keep them accurate to GMT. This practice changed in 1972. At this point, atomic clock time was set permanently and a system of leap seconds (positive or negative changes to the time on atomic clock) was introduced instead. This led to the development of Coordinated Universal Time (UTC).

The development of UTC and the use of leap seconds mean that now even though clocks still closely reflect local time, officials are able to alter atomic clocks in very simple ways in order to keep them coordinated with UTC. In fact, using leap seconds it is possible to keep Coordinated Universal Time within 0.9 seconds of Greenwich Mean Time (also known as UTC1).

Many countries adopt Daylight Savings Time. Because of changes to the time that occur twice annually, the local time at the Greenwich Observatory is only equal to UTC during the period from 1 a.m. UTC on the last Sunday in October to 1 a.m. UTC on the final Sunday in March. This is a situation which occurs in many countries around the world.


There have been a number of significant dates in the development of standardized time keeping. They began in 1675, when the Royal Observatory was constructed in Greenwich, England. It was constructed as a way of helping British mariners determine longitude at sea. Time was in no way standardized before this and even though there were timekeeping devices, town clocks were usually calibrated to noon local time on a daily basis. Unfortunately, this meant that every town had a time which was slightly different even if they were located near other towns.

Portable chronometers made it easier to keep accurate time. The British railway was actually the first organization to set up a specific time zone using these portable chronometers. It became known as railway time. In August of 1852 the telegraph system was used to send information about Greenwich Mean Time across the country. In August of 1880, GMT was adopted as the official time of Britain (but not Ireland).

In 1868, New Zealand established New Zealand Mean Time. It was set at 11 and a half hours ahead of GMT because of the longitudinal distance from Greenwich to New Zealand.

Time was not standardized for American railways the way it was for British railways until 1870. The idea, which was first proposed in 1863 by Charles F. Dowd involved four time zones that ran from north to south. Although it was a simple system, it was not adopted and a similar system was proposed by William F. Allen. It was this system, which involved time zone borders running through railway stations) which was accepted in American and Canadian railways. These time zones were named Eastern, Central, Mountain and Pacific, and were being used in approximately 85% of all cities with larger populations (over 10,000 people) were using this system.

A number of different people from different nationalities have proposed different methods of determining time zones. Italian Quirico Filopanti first proposed the idea of 24 time zones which were called “longitudinal days”. They were centred on the meridian in Rome but his system was not adopted and, in fact, when largely unnoticed by other experts.

In 1879, Canadian Sir Sanford Flemming proposed a system of time zones which could be implemented around the world. He also proposed a 24-hour clock that was not linked to any of the surface meridians as other clocks and time zone systems were.

By 1929, most of the major countries around the world were using the system of time zones. There are countries which do not use one hour time zones however. Some may use half-hour zones and a very few use fifteen minute zones.

There are also a few countries which still use a single time zone system even though they may be much wider than the normally accepted fifteen degree limit that marks the boundaries of one hour time zones.

Skewing of Zones

Each time zone tends to be centred on one of the Earth’s meridians. They are based on a fifteen degree width and so extend 7.5 degrees out on either side of the meridian. Although the lines are intended to be precise and even, there is often a difference between theory and practice and many time zones may have boundaries which are uneven or which fall outside of the accepted limits.

The Prime Meridian, the basis on which all time zones are founded, passes through Spain and France. However, instead of using GMT, they tend to use Central European Time (CET). This is because during German occupation during the Second World War, the time was changed to CET and no reversal of this change was made following the war.

Since some areas may not use Daylight Savings Time, this can lead to an even further skewing of zones as can the tendency of some countries such as China and India to use a single zone throughout their country. Because these countries are much wider than the fifteen degree range that is used for other time zones, this can cause some skewing and confusion.

Additional Information

• Many countries have more time zones than you may think possible. France, for example, has a total of twelve time zones. These are in part due to the time differences in colonies such as French Guyana and other French islands. Other countries with many time zones include Russia (eleven including ten contiguous zones and a separate one for the Baltic Sea town of Kaliningrad). The USA has ten time zones, followed by nine for Australia, eight for the UK and six in Canada).
• Of the countries with only one time zone, China is the largest. This was not always the case. Before 1949, the country actually had five time zones.
• Antarctica also goes by different time than you might otherwise think. Although the two research stations are American, they go by New Zealand time. This is UTC+12 hours in Southern winter and UTC+13 hours in Southern summer
• Although time zones are normally based on the Earth’s meridians, the 27°N latitude travels through several different time zones. Although the time zones should be one hour apart, the different countries tend to use different time zones and not all countries in the area are using sequential time zones. It is made even more complicated by the decision of Pakistan to adopt daylight savings time.
• On the globe, there is actually a 26-hour difference between the earliest and latest time zones. This means that it can be the same day for longer than an actual day is chronologically.
• There are areas on the Earth where three time zones may meet due to geography. One example of this is the border of Finland, Russia and Norway.
• Although a day is 24 hours long, there are actually 40 time zones. Because some zones are less than one hour different in time (such as half or quarter hour zones), this extends the number of total zones to 40.
• Although you would think that borders between countries would have time zones that are close to one another, there may be large gaps. The largest of these is the 3.5 hour difference which is located along the border between China and Afghanistan.
• There are time zones which are highly unusual. One of the most unusual is the Central Western Time Zone that is located in Australia. Although it covers an area larger than that of Belgium only about 200 people make their home within this zone. CWST is honoured and is also necessary in order to lessen the time gap between the border of Western Australia and Southern Australia.

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