In order to efficiently use and measure time, everyone in the world would like to fix noon as the time at which the sun is at its highest point in the sky (i.e. when it is crossing the meridian). However, this seems to be impossible without the use of time zones. Since the Earth rotates at the rate of 15 degrees every hour, the sun is at its highest point in the sky at different times in the day for different countries around the globe. The idea behind time zones is that we can divide the world into 24 equal slices or zones, 15 degrees each, and adjust the clocks accordingly for each zone. We can thus preserve the need to fix noon as the time when the sun is highest in the sky for each country and yet also make it easy to understand times between different zones. The person who famously proposed this was Sir Sanford Fleming, a Scottish-born Canadian, in the late 19th century. Although well-received, this system would only be instituted worldwide in 1929, establishing arguably the most crucial system of the modern world.
How does it all work?
Time zones are measured by reference to a specific point, namely the Greenwich Meridian. This is sometimes called the Prime Meridian, and it is located at the Royal Observatory in Greenwich, England. We have commonly referred to time at this point as Greenwich Mean Time or Universal Time (abbreviated as GMT), though in recent years it has been used to refer to the more accurate Coordinated Universal Time (abbreviated as UTC) which uses an atomic time scale. UTC is used as a starting point to determine time in other countries worldwide. So, for example, if a country is stated as having the time UTC+3, this means that when it is noon in Greenwich, it is 3pm in that country.
Buenos Aires: UTC-3
London (U.K.): UTC
Los Angeles: UTC-8
Mexico City: UTC-6
New Delhi: UTC+5.30
New York: UTC-5
Washington DC: UTC-5
The International Date Line
The International Date Line (IDL) is an imaginary line on the opposite side of the world from the Prime Meridian. It is 180 degrees both East and West from Greenwich, which means that on either side of the line it is a different day. This is because the IDL intersects the time zones which are UTC+12 and UTC-12. Even though the IDL mostly passes through the ocean, it could quite easily confuse travelers who experience a change in day just by crossing over. The position of the IDL has in fact changed several times since time zones were introduced. It has been made to zig-zag around countries so no one on land is affected, though this still creates problems for those flying or sailing through. Crossing it while traveling East means subtracting a day, and crossing it while traveling West means adding a day. To illustrate this often confusing notion, if you fly from Tonga to Samoa by air, the journey takes approximately two hours, but the passenger officially arrives the day before they left.
Interesting facts about time zones
It is said that the reason Greenwich is seen as an important point of reference is because of the existence of the Greenwich Observatory. A conference of astronomers in 1884 argued that this was an important landmark from which all calculations about time should be made. Interestingly enough, Greenwich remains the prime meridian even though the original observatory has moved elsewhere.
Even though most of the world's time zones differ by increments of an hour, there are many places around the world that use so-called 'offset' time zones. This means that the time zones differ from the standard time zone of that place by half an hour or even fifteen minutes. Examples of such countries are India (UTC+5.30) and Nepal (UTC+0545).
In terms of which country has the largest number of time zones, Russia comes out as having the most. It has eleven, including Kaliningrad on the Baltic Sea. China is also interesting as the largest country with only one time zone (UTC+8).
If we adopted the standard technique of time zones at the poles, this would be very problematic. Since longitude lines narrow at the poles, each segment would become very narrow and very small areas would differ in time. Therefore, people who live or work at the North and South Poles simply use UTC time.
Advice for travelers
Travelers should make sure that before they go to a different country, they check the difference in time there and change clocks accordingly when they arrive (and back to the original when they come back). They should also note that not all countries have the same time. Many countries such as USA span multiple time zones.
A confusion for travelers is often generated by the fact that many countries use Daylight Saving Time (often referred to as DST or Summer Time). Daylight Saving Time is used in many places around the world and it means adjusting local clocks in order to make the most use of available natural light during the summer months.
Many travelers find that they suffer from a condition known as 'jet lag' when they have crossed time zones. This is a physiological condition triggered by the body becoming out of sync with the usual light and dark patterns to which it is accustomed. The condition is characterized by numerous symptoms, such as extreme fatigue, disorientation and loss of appetite. Jet lag often takes many days to recover; a rough medical guideline being one day per time zone. Sleep is seen as one of the best cures for jet lag, as is exposure to sunlight.