According to our map of the world’s time zones the country spanning the greatest number of time zones is Russia. From east to west, Russia spans 11 zones, but groups them into 8 standard time zones. China covers 5 time zones but runs on a single national time using the standard meridian of Beijing.
A few countries, such as India and Iran, keep time using a meridian that is positioned midway between standard meridians, so that their clocks depart from those of their neighbors by 30 or 90 minutes. Some states or provinces within countries also keep time by 7½° meridians, such as the Canadian province of Newfoundland and the interior Australian states of South Australia and Northern Territory.
World time zones are often referred to by number to indicate the difference in hours between time in a zone and time in Greenwich. A number of –7, for example, indicates that local time is seven hours behind Greenwich time, while a 13 indicates that local time is three hours ahead of Greenwich time.
INTERNATIONAL DATE LINE
Take a world map or globe with 15° meridians. Start at the Greenwich 0° meridian and count along the 15° meridians in an eastward direction. You will find that the 180th meridian is number 12 and that the time at this meridian is, therefore, 12 hours later than Greenwich time. Counting in a similar manner westward from the Greenwich meridian, we find that the 180th meridian is again number 12 but that the time is 12 hours earlier than Greenwich time. We seem to have a paradox:
How can the same meridian be both 12 hours ahead of Greenwich time and 12 hours behind it? The answer is that each side of this meridian is experiencing a different day.
Imagine that you are on the 180° meridian on June 26. At the exact instant of midnight, the same 24-hour calendar day covers the entire globe.
Stepping east will place you in the very early morn-ing of June 26, while stepping west will place you very late in the evening of June 26. You are on the same calendar day on both sides of the meridian but 24 hours apart in time.
Doing the same experiment an hour later, at 1:00 a.m., stepping east you will fi nd that you are in the early morning of June 26. But if you step west, you will fi nd that midnight of June 26 has passed, and it is now the early morning of June 27. So on the west side of the 180th meridian, it is also 1:00 a.m. but it is one day later than on the east side. For this reason, the 180th meridian serves as the International Date Line . This means that if you travel westward across the date line, you must advance your calendar by one day. If traveling eastward, you set your calendar back by a day.
Air travelers on Pacific routes between North America and Asia cross the date line. For example, flying westward from Los Angeles to Sydney, Australia, you may depart on a Tuesday evening and arrive on a Thursday morn-ing after a flight that lasts only 14 hours. On an east-ward flight from Tokyo to San Francisco, you may actually arrive the day before you take off, taking the date change into account!
Actually, the International Date Line does not follow the 180th meridian exactly. Like many time zone boundaries, it deviates from the meridian for practical reasons. As shown in figure, it has a zigzag offset between Asia and North America, as well as an eastward offset in the South Pacific to keep clear of New Zealand and several island groups.
DAYLIGHT SAVING TIME
The United States and many other countries observe some form of daylight saving time , in which clocks are set ahead by an hour (sometimes two) for part of the year. Although it was once thought that adding daylight hours to the end of the workday would save electricity and reduce traffic accidents and crime, the evidence now shows that the primary effects are eco-nomic—allowing more retail shopping and recreation, for example. Although something of a mixed blessing, daylight saving time is now a part of normal life in most places.
In the United States, daylight saving time comes into effect on the second Sunday in March and is dis-continued on the first Sunday of November. Arizona (except the Navajo Nation), Puerto Rico, Hawaii, U.S.
Virgin Islands, Guam, the Northern Mariana Islands, and American Samoa do not observe daylight saving time. Although many other nations observe daylight saving time, they do not always begin and end it on the same days of the year. In the European Union, daylight saving time is called summer time . It begins on the last Sunday in March and ends on the last Sunday in October.
Since the 1950s, the most accurate time has been kept using atomic clocks, which are based on the frequency of microwave energy emission from atoms of the element cesium cooled to near absolute zero. These very accurate clocks keep time to better than one part in 1 trillion. Atomic time is a universal standard that is not related to the Earth ’s rotation. Civil time sources use Coordinated Universal Time (UTC), which is derived from atomic time and provides a day of 86,400 seconds (24 hours) in length to match the Earth ’s mean rotation rate with respect to the Sun. Coordinated Universal Time is administered by the Bureau International de l ’Heure, located near Paris.
Our Earth is a much less precise timekeeper, exhibiting small changes in the angular velocity of its rotation on its axis and variations in the time it takes to complete one circuit around the Sun. As a result, constant adjustments to the timekeeping system are necessary.
INDIA NEED ADDITIONAL TIME ZONE?
India’s single time zone, which causes problems for easterners who face summer sunrise as early as 4:30am.
Despite India’s vast size, it has one time of +5:30 from Greenwich Mean Time for its 1.2-billion population, spread from points further east than Bangladesh to the western Arabian Sea.
At this time of year the sun rises in the east shortly before 6am, more than 90 minutes earlier than in the west, while daybreak in the east comes as early as 4:30am around the summer solstice.
“We need a local time for Assam and the other northeastern states which will be ahead of the Indian Standard Time (IST) by at least an hour to 90 minutes,” said Mr.Tarun Gogoi, Chief minister of Assam. “We have an early daybreak in the northeast compared to other parts of India and if we have a separate time zone then it would undoubtedly be very productive for all of us and would also help in saving energy,” he added.
He plans to lobby in New Delhi for a change, renewing a campaign which last gathered momentum in 2010.
Mr Gogoi says sticking to Indian Standard Time means a loss of daylight hours and an attendant decrease in productivity for his state. For instance, a farmer in Assam can start work one hour before her or his counterpart in a state like Gujarat
He points out that tea gardens in Assam have for years set their clocks an hour ahead of the rest of the country.
The proposal for a different time zone will have to be cleared by the Centre.