Time Zone.

[satish]

Time Zone.
A time zone is a region of the Earth that has adopted the same standard time, usually referred to as the local time.

Standard time zones can be defined by geometrically subdividing the Earth's spheroid into 24 lunes (wedge-shaped sections), bordered by meridians each 15° of longitude apart. The local time in neighbouring zones would differ by one hour. However, political and geographical practicalities can result in irregularly-shaped zones that follow political boundaries or that change their time seasonally (as with daylight saving time), as well as being subject to occasional redefinition as political conditions change.

Greenwich Mean Time (GMT) was established in 1675, when the Royal Observatory was built, as an aid to determine longitude at sea by mariners. The first time zone in the world was established by British railways on December 1, 1847 — with GMT hand-carried on chronometers.
About August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory, Greenwich. Even though 98% of Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880. Some old clocks from this period have two minute hands — one for the local time, one for GMT.

This only applied to the island of Great Britain, and not to the island of Ireland.

On November 2, 1868, New Zealand (then a British colony) officially adopted a standard time to be observed throughout the colony, and was perhaps the first country to do so.
It was based on the longitude 172° 30' East of Greenwich, that is 11 hours 30 minutes ahead of GMT. This standard was known as New Zealand Mean Time.

most major countries had adopted hourly time zones by 1929. Today, all nations use standard time zones for secular purposes, but they do not all apply the concept as originally conceived.

Newfoundland, India, Iran, Afghanistan, Venezuela, Burma, the Marquesas, as well as parts of Australia use half-hour deviations from standard time, and some nations, such as Nepal, and some provinces, such as the Chatham Islands, use quarter-hour deviations.

Time Zone for the Navigation purpose.

A ship within the territorial waters of any nation would use that nation's standard time, but would revert to nautical standard time upon leaving its territorial waters.
The captain was permitted to change his ship's clocks at a time of his choice following his ship's entry into another time zone—he often chose midnight.
For airplanes, similar principles apply.

DST(Daylight saving time)
Many countries, or even parts only of countries, adopt daylight saving time during part of the year. This typically involves advancing clocks by an hour near the start of spring and adjusting back in autumn.
Some countries also use backward daylight saving over the winter period. Modern DST was first proposed in 1907 and was widespread use in 1916 as a wartime measure aimed at conserving coal. Despite controversy, many countries have used it since then.

Some facts about time zone.

1) Russia has the largest number of time zones: eleven, including Kaliningrad on the Baltic Sea. In terms of distinct time zones, Canada and the United States are tied for second with six, while Australia has seven time zones that always overlap to some degree

2) If the possessions of the United Kingdom, the United States and France are included it increases the number of time zones in each. Taking into account overseas territories and possessions, France has the most, with at least twelve time zones, followed by Australia with ten, the United States with nine and the United Kingdom with at least eight.

3) In terms of area, China is the largest country with only one time zone (UTC+8). Before the Communist control of the mainland in 1949 during the Chinese Civil War, China was separated into five time zones. China also has the widest spanning time zone.

4) There are numerous places where several time zones meet, for instance at the tri-country border of Finland, Norway and Russia.

5) The largest time gap along a political border is the 3.5 hour gap along the border of China

Source-wikipedia

[sivaharimani]

thats a good post sathis. you have done it soon. infact, i had an idea to post on time zones. even If i would have done so, it would not be greater than your information.. thanks for sharing

[kushal]

Can You guys explain more about Daylight Saving Time?

[sivaharimani]

Daylight Saving Times(DST)

Daylight saving time (DST; also summer time in British English) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1907 by William Willett. Many countries have used it since then; details vary by location and change occasionally.

The practice can be controversial.Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours, but causes problems for farming, entertainment and other occupations tied to the sun. Extra afternoon daylight reduces traffic fatalities;its effect on health and crime is less clear. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity;changes in usage patterns have cast doubt on whether DST now saves energy.

DST's clock shifts can serve as fire safety reminders,but they complicate timekeeping and can disrupt meetings, travel, billing, recordkeeping, medical devices, and heavy equipment.Many computer-based systems can adjust their clocks automatically, but this can be limited and error-prone, particularly when DST rules change.

One of the biggest reasons we change our clocks to Daylight Saving Time (DST) is that it saves energy. Energy use and the demand for electricity for lighting our homes is directly connected to when we go to bed and when we get up. Bedtime for most of us is late evening through the year. When we go to bed, we turn off the lights and TV.

In the average home, 25 percent of all the electricity we use is for lighting and small appliances, such as TVs, VCRs and stereos. A good percentage of energy consumed by lighting and appliances occurs in the evening when families are home. By moving the clock ahead one hour, we can cut the amount of electricity we consume each day.

Studies done in the 1970s by the U.S. Department of Transportation show that we trim the entire country's electricity usage by about one percent EACH DAY with Daylight Saving Time.

Daylight Saving Time "makes" the sun "set" one hour later and therefore reduces the period between sunset and bedtime by one hour. This means that less electricity would be used for lighting and appliances late in the day.

We also use less electricity because we are home fewer hours during the "longer" days of spring and summer. Most people plan outdoor activities in the extra daylight hours. When we are not at home, we don't turn on the appliances and lights. A poll done by the U.S. Department of Transportation indicated that Americans liked Daylight Saving Time because "there is more light in the evenings / can do more in the evenings."

Daylight Saving Time Saves Energy

While the amounts of energy saved per household are small...added up they can be very large.

In the winter, the afternoon Daylight Saving Time advantage is offset by the morning's need for more lighting. In spring and fall, the advantage is less than one hour. So, Daylight Saving Time saves energy for lighting in all seasons of the year except for the four darkest months of the year (November, December, January and February) when the afternoon advantage is offset by the need for lighting because of late sunrise.

A report was released in May 2001 by the California Energy Commission to see if creating an early DST or going to a year-round DST will help with the electricity problems the state faced in 2000-2001-2002. You can download an Acrobat PDF copy of the staff report, Effects of Daylight Saving Time on California Electricity Use, Publication # 400-01-13.

The study concluded that both Winter Daylight Saving Time and Summer-season Double Daylight SavingTime (DDST) would probably save marginal amounts of electricity - around 3,400 megawatt-hours (MWh) a day in winter (one-half of one percent of winter electricity use - 0.5%) and around 1,500 MWh a day during the summer season (one-fifth of one percent of summer-season use - 0.20%). Winter DST would cut winter peak electricity use by around 1,100 megawatts on average, or 3.4 percent. Summer Double DST would cause a smaller (220 MW) and more uncertain drop in the peak, but it could still save hundreds of millions of dollars because it would shift electricity use to low demand (cheaper) morning hours and decrease electricity use during higher demand hours.

The model used in the Energy Commission's study is now being used by the U.S. Department of Energy in a larger national study of daylight saving time. It's unknown when that study will be completed.

History of Daylight Saving Time

Daylight Saving Time is a change in the standard time of each time zone. Time zones were first used by the railroads in 1883 to standardize their schedules. According to the The Canadian Encyclopedia Plus by McClelland & Stewart Inc., Canada's "[Sir Sandford] Fleming also played a key role in the development of a worldwide system of keeping time. Trains had made obsolete the old system where major cities and regions set clocks according to local astronomical conditions. Fleming advocated the adoption of a standard or mean time and hourly variations from that according to established time zones. He was instrumental in convening an International Prime Meridian Conference in Washington in 1884 at which the system of international standard time -- still in use today -- was adopted."

In 1918, the U.S. Congress made the U.S. rail zones official under federal law and gave the responsibility to make any changes to the Interstate Commerce Commission, the only federal transportation regulatory agency at the time. When Congress created the Department of Transportation in 1966, it transferred the responsibility for the time laws to the new department.

The American law by which we turn our clock forward in the spring and back in the fall is known as the Uniform Time Act of 1966. The law does not require that anyone observe Daylight Saving Time; all the law says is that if we are going to observe Daylight Saving Time, it must be done uniformly.

Daylight Saving Time has been around for most of this century and even earlier.

Benjamin Franklin, while a minister to France, first suggested the idea in an essay titled "An Economical Project for Diminishing the Cost of Light." The essay was first published in the Journal de Paris in April 1784. But it wasn't for more than a century later that an Englishman, William Willett, suggested it again in 1907.

Willett was reportedly passing by a home where the shades were down, even though the sun was up. He wrote a pamphlet called "The Waste of Daylight" because of his observations.

Willett wanted to move the clock ahead by 80 minutes in four moves of 20 minutes each during the spring and summer months. In 1908, the British House of Commons rejected advancing the clock by one hour in the spring and back again in the autumn.

Willett's idea didn't die, and it culminated in the introduction of British Summer Time by an Act of Parliament in 1916. Clocks were put one hour ahead of Greenwich Mean Time (GMT) during the summer months.

England recognized that the nation could save energy and changed their clocks during the first World War.

In 1918, in order to conserve resources for the war effort, the U.S. Congress placed the country on Daylight Saving Time for the remainder of WW I. It was observed for seven months in 1918 and 1919. The law, however, proved so unpopular that it was later repealed.

When America went to war again, Congress reinstated Daylight Saving Time on February 9, 1942. Time in the U.S. was advanced one hour to save energy. It remained advanced one hour forward year-round until September 30, 1945.

In England, the energy saving aspects of Daylight Saving were recognized again during WWII. Clocks were changed two hours ahead of GMT during the summer, which became known as Double Summer Time. But it didn't stop with the summer. During the war, clocks remained one hour ahead of GMT though the winter.

From 1945 to 1966, there was no U.S. law about Daylight Saving Time. So, states and localities were free to observe Daylight Saving Time or not.

This, however, caused confusion -- especially for the broadcasting industry, and for trains and buses. Because of the different local customs and laws, radio and TV stations and the transportation companies had to publish new schedules every time a state or town began or ended Daylight Saving Time.

By 1966, some 100 million Americans were observing Daylight Saving Time through their own local laws and customs. Congress decided to step in end the confusion and establish one pattern across the country. The Uniform Time Act of 1966 (15 U.S. Code Section 260a) created Daylight Saving Time to begin on the last Sunday of April and to end on the last Sunday of October. Any area that wanted to be exempt from Daylight Saving Time could do so by passing a local ordinance. The law was amended in 1986 to begin Daylight Saving Time on the first Sunday in April.

concluded facts

Daylight Saving Time saves energy. Based on consumption figures for 1974 and 1975, The Department of Transportation says observing Daylight Saving Time in March and April saved the equivalent in energy of 10,000 barrels of oil each day -- a total of 600,000 barrels in each of those two years. California Energy Commission studies confirm a saving of about one percent per day.


Daylight Saving Time saves lives and prevents traffic injuries. The earlier Daylight Saving Time allowed more people to travel home from work and school in daylight, which is much safer than darkness. And except for the months of November through February, Daylight Saving Time does not increase the morning hazard for those going to school and work.


Daylight Saving Time prevents crime. Because people get home from work and school and complete more errands and chores in daylight, Daylight Saving Time also seems to reduce people's exposure to various crimes, which are more common in darkness than in light.

the countries under DST system

Daylight Saving Time Around the World 2007

Various time zones of various countries

Daylight Saving Time and Daylight Saving Time map for countries and territories 2008-2009

SOURCE - TIME AND DATE