The term Time Zone and the number of standard time zones is debatable and discussed among various sources. We generally don’t discuss a lot about time zones in our daily routine life. Below are some common definitions and terms which we can get from different sources debating and defining Time Zone. Here in this article I have tried to put all the references from different articles and websites together at one place to understand not all but at least get the basic idea and most widely accepted term of what Time Zone is and Why it is Important. Any corrections, suggestions and additions to this are most Welcome.
- A time zone is a region that has a uniform standard time for legal, commercial, and social purposes. It is convenient for areas in close commercial or other communication to keep the same time, so time zones tend to follow the boundaries of countries and their subdivisions.
Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12 to UTC+14), but a few are offset by 30 or 45 minutes. Some higher latitude countries use daylight saving time for part of the year, typically by changing clocks by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight saving time effect.
- A ‘Time Zone’ refers to any of 24 regions loosely divided by longitude, where the same standard time is kept.
The Greenwich Meridian, also known as The Prime Meridian or International Meridian, or 0º longitude is the ‘starting point’ for dividing the Earth’s surface into time zones. Each time zone is 15 degrees of longitude wide (with local variations) and the local time is one hour earlier than the zone immediately to the east on the map.
Simply we can say that it is important as
Time zones are a geographical region and globe division of 15o each, starting at the Prime Meridian or Zero Degree longitude at Greenwich, in England which is created to help people know what time is it now in another part of the world, where just about everybody observes the same standard time.
A time offset is an amount of time subtracted from or added to UTC to get the current civil time or local time, whether it’s standard time or Daylight saving time.
In any particular time zone residents either observes standard time all year or they observe standard time in winter and daylight time in summer.
Most commonly Time Zones are represented by 3 or 4 letters and are usually defined by your country government or some astronomical institute.
Coordinated Universal Time commonly known as UTC is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time (GMT). For most purposes, UTC is considered interchangeable with GMT, but GMT is no longer precisely defined by the scientific community.
Daylight saving time (DST) or summer time is generally advancing clocks during summer months. Typically, users of DST adjust their clocks one hour forward near the start of spring and again adjust them backward in the autumn to normal or regular time. One of the important reasons considered for creating DST is energy savings. Simply, it is only a change of Time Zone and the primitive time (UTC) is still and will always be the same.
Greenwich Mean Time (GMT) refers to the mean solar time at the Royal Observatory in Greenwich, London, which became adopted as a global time standard. Coordinated Universal Time (UTC) is arranged so that it runs no more than 0.9 seconds fast or slow of Greenwich Mean Time. The name Greenwich Mean Time is especially used by bodies connected with the United Kingdom and others particularly in Arab countries. It is a term commonly used in the United Kingdom and countries of the Commonwealth, including Australia, New Zealand, South Africa, India, Pakistan and Malaysia, and many other countries in the Eastern hemisphere.
Greenwich Mean Time is the same as Universal Time (UT), a standard astronomical concept used in many technical fields. In the United Kingdom, GMT is the official time during winter; during summer British Summer Time (BST) is used. GMT is very close to Western European Time.
IANA time zone database
The IANA time zone database maps a name to the named location’s historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, and the Oracle RDBMS; HP’s “tztab” database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in TZ=’:America/New York’. In many of those systems there is also a system-wide setting that is applied if the TZ environment variable isn’t set: this setting is controlled by the contents of the /etc/local time file, which is usually a symbolic link or hard link to one of the zoneinfo files. Internal time is stored in timezone-independent epoch time; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.
Internet and Computers
Computer operating systems include the necessary support for working with all or almost all possible local times based on the various time zones. Internally, operating systems typically use UTC as their basic time-keeping standard, while providing services for converting local times to and from UTC, and also the ability to automatically change local time conversions at the start and end of daylight saving time in the various time zones.
Web servers presenting web pages primarily for an audience in a single time zone or a limited range of time zones typically show times as a local time, perhaps with UTC time in brackets. More internationally oriented websites may show times in UTC only or using an arbitrary time zone.
Email systems and other messaging systems time-stamp messages using UTC, or else include the sender’s time zone as part of the message, allowing the receiving program to display the message’s date and time of sending in the recipient’s local time.
Database records that include a time stamp typically use UTC, especially when the database is part of a system that spans multiple time zones. The use of local time for time-stamping records is not recommended for time zones that implement daylight saving time due to the fact that once a year there is a one hour period when local times are ambiguous.
The Basic Concept
It is said that before the advent of railways in the 1800s, all time was local. Noon was simply when the sun was directly overhead wherever you were, in what is called solar time. Each town’s citizens would set their clocks and pocket watches on observing the sun and the stars or according to the official town clock or timekeeper. When they traveled to another town, they would simply change their watch when they arrived. However, time differences between distant locations were barely noticeable because of long travel times and the lack of long-distance communications. The expansion of transport and communications, as well as trade globalization, thus created a need for a more unified time-keeping system.
Moreover, various meridians were also used for longitudinal reference among different countries. The Greenwich Meridian was adopted in 1884 as the initial or prime meridian for longitude and timekeeping.
In 1878, Sir Sandford Fleming (1827–1915) developed the system of worldwide time zones that we still use today. He proposed that the world be divided into 24 time zones, each 15º wide of longitude apart. He came to this idea because Earth completes a rotation every 24 hours and there are 360º of longitude, so each hour Earth rotates 1/24th of a circle or 15º.
How Time Zones Works
The Earth spins on an imaginary pole called its axis. The Earth makes a complete rotation or one full turn on its axis every 24 hours. We call each full turn or rotation as a day. The Earth moves 15 degrees longitude each hour and Time zones are primarily based on this same fact. Since there are 24 hours in a day there are 24 standard time zones. (24 hours x 15º=360º). The Prime Meridian or 0º longitude is used as starting point to count Time zones. Each time zone is counted at 15 º intervals and extends 7½º either side of a central meridian.
Corresponding to a one-hour difference in mean solar time, each time zone is theoretically 15º wide. We see that generally to match internal and international borders, the shape of time zones is changed. Civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks, changes by one hour forward and backward respectively for every 15º east or west of the Greenwich Meridian. One would need to divide the longitude, in degrees, by 15 to find the appropriate time zone, in hours.
As stated in my previous articles www.timezdb.com provides World Time Zone database and API for developers free to use on your websites and applications. Please do visit.