Local and Standard Time and the International Date Line
Local Time
- The time at a particular place with reference to the overhead position of the sun in the sky is considered as the local time of that place.
- Local time of a particular place is determined by the mid-day sun. All places on the same meridian experience noon at the same time.
- As the Earth rotates 360º in 24 hours, in 1 hour it would rotate 360º/24º or 15º.
- Similarly, the earth would take 4 minutes to rotate 1º.
- Therefore, when it is midday at a particular place, the time would differ by 4 minutes for each degree of longitude east or west of that meridian.
- As the Earth rotates from west to east, places to the east see the sun first and so the time is ahead, while places to the west see the sun later and so are behind the time.
- Hence, if the time at Greenwich or 0º meridian is noon, it would be 12.04 pm at 1º E and 11.56 am at 1º W and similarly it would be11 am at 15º W and 1 pm at 15º E.
- Thus, each country has many local times and larger the E-W extent, the more the differences in local times.
Standard Time
- Standard time is the local time in a country or region when Daylight Saving Time (DST) is not in use.
- Standard time is sometimes referred to as or winter time or normal time, while DST may also be called summer time, especially in the UK.
- More than 60% of the countries in the world use standard time all year.
- The remaining countries use DST during the summer months, generally setting clocks forward 1 hour from standard time.
- Standard Time is the time of a region or country that is established by law or general usage as civil time.
- The concept was adopted in the late 19th century in an attempt to end the confusion that was caused by each community’s use of its own solar time.
- Some such standard became increasingly necessary with the development of rapid railway transportation and the consequent confusion of schedules that used scores of different local times kept in separate communities. (Local time varies continuously with change in longitude.)
- The need for a standard time was felt most particularly in the United States and Canada, where long-distance railway routes passed through places that differed by several hours in local time.
- Sir Sandford Fleming, a Canadian railway planner and engineer, outlined a plan for worldwide standard time in the late 1870s.
- Following this initiative, in 1884 delegates from 27 countries met in Washington, D.C., and agreed on a system basically the same as that now in use.
- The present system employs 24 standard meridians of longitude (lines running from the North Poleto the South Pole, at right angles to the Equator) 15° apart, starting with the prime meridian through Greenwich, England.
- These meridians are theoretically the centres of 24 Standard Time zones, although in practice the zones often are subdivided or altered in shape for the convenience of inhabitants; a notable example of such alteration is the eastward extension of the International Date Linearound the Pacific island country of Kiribati.
- Time is the same throughout each zone and differs from the international basis of legal and scientific time, Coordinated Universal Time, by an integralnumber of hours; minutes and seconds are the same.
- In a few regions, however, the legal time kept is not that of one of the 24 Standard Time zones, because half-hour or quarter-hour differences are in effect there.
- In addition, Daylight Saving Time is a common system by which time is advanced one hour from Standard Time, typically to extend daylight hours during conventional waking time and in most cases for part of the year (usually in summer).
Indian Standard Time
About Indian Standard Time
- Indian Standard Time(IST) represents the time observed throughout India, with a time offset of UTC+5:30. India opted out of observing daylight saving time, (DST) or other seasonal adjustments, although briefly using DST during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971.
- In military and aviation time, E*(“Echo-Star”) designates IST.
- Indian Standard Time calculates on the basis of 82.5° E longitude, just west of the town of Mirzapur, near Allahabad in the state of Uttar Pradesh.
- The longitude difference between Mirzapur and the United Kingdom’s Royal Observatory at Greenwich translates to an exact time difference of 5 hours 30 minutes.
- A clock tower at the Allahabad Observatory (15° N 82.5° E) calculates local time, though the National Physical Laboratory, in New Delhi has been entrusted with the official time-keeping devices.
History of IST
- Most towns in India retained their own local time until a few years after the introduction of the railways in the 1850s, when the need for a unified time zone became apparent.
- Local time in Mumbai(then Bombay) and Kolkata (then Calcutta), as headquarters of the two largest Presidencies of British India, assumed special importance, the nearby provinces and princely states gradually adopted the standard.
- In the 19th century, telegraphkept the clocks in synchronization– for example the railways synchronized their clocks thorough a time signal sent from the head office or the regional headquarters at a specified time every day.
- In 1884, the International Meridian Conference in Washington, D.C.set up uniform time zones across the world, India receiving two time zones, with Calcutta using the 90th east meridian and Bombay the 75° E meridian.
- The Conference set Calcutta time at 5 hours 30 minutes 21 seconds ahead of GMT, while setting Bombay time at 4 hours 51 minutes ahead.
- By the late 1880s, many railway companies began to use Madras time (known as “Railway time”) as an intermediate time between the two zones.
- The British colonial government established another time zone, Port Blair mean time, established at Port Blair, the capital of the Andaman and Nicobar Islands in the Bay of Bengal.
- They set Port Blair mean time to 49 minutes 51 seconds ahead of Madras time.
- British Indiaofficially adopted the standard time zones in 1905, when picking the meridian passing east of Allahabad at 82.5° E longitude as the central meridian for India, corresponding to a single time zone for the country.
- That came into force on January 1, 1906, also applying to Sri Lanka (then Ceylon). Calcutta time remained as an official, separate time zone until 1948.
IST in relation with the bordering nations
- In 1925, the government began relaying time synchronization through omnibus telephone systems and control circuits to organizations that needed to know the precise time. That continued until the 1940s, when the government began to broadcast time signals using the radio.
- After independence in 1947, the Indian government established IST as the official time for the whole country, although Kolkata and Mumbai retained their own local time for a few more years.
- The Central observatory moved from Chennai to a location near Mirzapur, as close as possible to UTC +5:30.
- During the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971, the government resorted briefly to daylight saving time as a way of reducing civilian energy consumption.
Issues with IST
- The country’s east–west distance of more than 2,000 km (1,200 miles) covers over 28 degrees of longitude, resulting in the sun rising and setting almost two hours earlier in the north-eastern Seven Sister States than in the Rann of Kutch in the far west.
- In the late 1980s, a team of researchers proposed separating the country into two or three time zones to conserve energy.
- The binary system that they suggested involved a return to British–era time zones; the government rejected the recommendations adopted
- In 2001, the government established a four–member committee under the Ministry of Science and Technology to examine the need for multiple time zones and daylight saving.
- The findings of the committee, presented to Parliament in 2004 by the Minister for Science and Technology, Kapil Sibal, recommended maintaining the current unified system, stating that “the prime meridian was chosen with reference to a central station, and that the expanse of the Indian State was not large.”
- Though the government has consistently refused to split the country into multiple time zones, provisions in labour laws such as the Plantations Labour Act, 1951allow the Central and State governments to define and set the local time for a particular industrial area.
- An August 2007 article in the Current Sciencejournal estimated that the evening peak energy demand could be reduced by as much as 16 percent by setting Indian Standard Time six hours ahead of Universal Coordinated Time instead of the present 5.5 hours.
- According to the authors, the money value of the savings accrued as a result of the time change would be in the range of Rs 1,000 crore every year.
Time signals
- The Time and Frequency Standards Laboratory at the National Physical Laboratory in New Delhi generate official time signals for both commercial and official use.
- The signals, based on atomic clocks, synchronize with the worldwide system of clocks that support the Coordinated Universal Time.
- Features of the Time and Frequency Standards Laboratory include:
- Four caesium and rubidium atomic clocks
- High frequency broadcast service operating at 10 MHz under call sign ATA to synchronize the user clock within a millisecond
- Indian National Satellite System satellite–based standard time and frequency broadcast service, which offers IST correct to ±10 microsecond and frequency calibration of up to ±10−10
- Time and frequency calibrations made with the help of pico– and nanoseconds time interval frequency counters and phase recorders
- The state–owned All India Radio and Doordarshan television network broadcast the exact time.
- Telephone companies have dedicated phone numbers connected to mirror time servers that also relay the precise time.
- Obtaining the time through Global Positioning System(GPS) receivers offers another increasingly popular method.
Daylight Saving Time
Daylight Saving Time, also called summer time, is the system for uniformly advancing clocks, so as to extend daylight hours during conventional waking time in the summer months. In countries in the Northern Hemisphere, clocks are usually set ahead one hour in late March or in April and are set back one hour in late September or in October.
About DST
- The practice was first suggested in a whimsical essay by Benjamin Franklinin 1784.
- Several countries, including Australia, Great Britain, Germany, and the United States, adopted summer Daylight Saving Time during World War Ito conserve fuel by reducing the need for artificial light.
- DST is in practice in some 70 countries, including those in the European Union.
- India does not follow daylight saving time; countries near the Equator do not experience high variations in daytime hours between seasons. (There is, however, a separate debate around the logic of sticking with only one time zone in a country as large as India.)
- In the US, it is practiced everywhere except in Hawaii and most of Arizona. In Australia, DST is observed in New South Wales, Victoria, South Australia, and Tasmania besides some other, smaller territories; and not observed in Queensland and Western Australia among other territories.
Objectives for using DST
- Achieve energy efficiency: Increasing focus on energy efficiency due to climate change because of over consumption of energy makes DST relevant. DST is thus environmentally sustainable concept.
- To ensure that the clocks show a later sunrise and later sunset — in effect ensure a longer evening daytime.
- Completion of routine work an hour earlier.
- DST is meant to save energy.
DST role in economy of an area
Possible Positive role:
On energy consumption:
- Energy is an important sector of the economy that creates jobs and value and extends its reach into economy thus contributes to economic growth and daylight saving time has its purported effect on energy usage.
- A report presented by S Department of Energy to Congress concluded that four week extension of daylight time saved about 0.5% of the nation’s electricity per day.
On Retail:
- Those who benefit most from DST are the retailers, sporting goods makers, and other businesses that benefit from extra afternoon sunlight.
- Having more hours of sunlight in between the end of the typical workday and bedtime induces customers to shop and to participate in outdoor afternoon sports.
- In 1984, Fortunemagazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores
On leisure sector:
- The National Golf Foundationestimated the extension would increase golf industry revenues $200 million to $300 million.
- A 1999 study estimated that DST increases the revenue of the European Union‘s leisure sector by about 3%.
On human capital:
- As we know economic impact of a better health could add $12 trillion to global GDP in 2040 and DST can significantly contribute to it as DST proponents argue the benefits of longer evenings in providing healthier lifestyle and a better healthy society.
Increased safety:
- Crime rates and traffic accidents decrease as a result of less evening activity in the dark
Possible negative role:
On Agriculture sector:
- DST can harm some farmers and others whose hours are set by the sun. One reason why farmers oppose DST is that grain is best harvested after dew evaporates, so when field hands arrive and leave earlier in summer, their labor is less valuable.
- Dairy farmers are another group who complain of the change due to DST. Their cows are sensitive to the timing of milking, so delivering milk earlier disrupts their systems.
On energy consumption:
- Critics of DST argue lights have become increasingly efficient, so lighting is responsible for a smaller chunk of total energy consumption than it was a few decades ago. Heating and cooling probably matter more, and some places may need air-conditioning for the longer, hotter evenings of summer daylight saving time.
Loss of workdays due to injuries:
- A studyof mining injuries across the U.S., found that there was a spike in workplace injuries of nearly 6 percent on the Monday following the shift to daylight saving time.
- An even greater cause for concern is that the severity of these injuries, as measured by days of work lost because of the injuries, increased by a whopping 67 percent, representing 2,600 more workdays lost, simply because of injuries experienced on that one day.
On labour and work productivity:
- Workplace productivity the week after DST drastically decreases. People are tired and lethargic due to a reduction in sleep.
- For instance, a slight drop in stock market performance is usually observed after the switch
- On human health affecting human capital:
- DST increases the risk of heart attack by 25%, while a return to original times lowers the risk by 21%.
- The disrupted sleep patterns might affect memory, learning, social interactions and overall cognitive performance.
- Several health problems as a result of disruption of the circadian rhythm (body clock)
On accidents:
- One hour of lost sleep in the US, one study calculated, increases the fatal crash rate by 5.4% to 7.6% for six days following the transition.
International Date Line
- The International Date Line (IDL) is an imaginary line that runs from the North to the South Pole and separates two calendar days.
- The IDL is important in measuring time and is crucial for instantaneous communication, politics, and commerce.
- The IDL is an imaginary line that roughly follows the 180° line of longitude and passes through the Pacific Ocean.
- However, this line is not straight and strays from the 180° meridian at certain points.
- In some places, it appears as zig-zag, deviating to the meridian’s east or west.
- The deviations enable places of the same economic and political affiliations to share the same date or time.
- Otherwise, if the IDL were a straight line, it would divide certain landmasses into two parts with two different dates on the same day.
- From the North Pole, the IDL first bends to the east to pass near the Chukchi Peninsula (Russia) and Wrangel Island’s east, then proceeds through the Bering Straitbefore bending towards the west of St. Matthew and St. Lawrence Islands.
- From there, the line runs between the Commander Islands and the Aleutian Islands and returns to the 180° meridian until it passes the equator.
- Below the equator, the line swings far to the east, near the 150° meridian, and circumscribes Kiribati.
- It then returns westward but remains to the 180° longitude’s east, passing through American Samoaand Samoa.
- Finally, the line bends southwestwards and follows the 180° meridian until it reaches Antarctica.
Why The 180° Meridian?
- The IDL was established in 1884 by the International Meridian Conference as an imaginary line roughly following the 180° meridian and not any other meridian (including the Prime Meridian).
- The conference, attended by 26 nations, settled on 180° longitude because it runs through an open ocean (Pacific Ocean) and zig-zagged it to keep the surrounding nations, especially island countries, within the same day and date.
Time and date across IDL
- When you cross the IDL, you either gain or lose a day depending on which way you are traveling.
- If you are traveling westward, you gain a day, and if you are traveling eastward, you lose a day.
- For example, if a traveler moves eastward across the Pacific Ocean from Wake Island to the Hawaiian Islands on June 25, they will jump backward to June 24 as soon as they cross the IDL. If, however, they are traveling in the opposite direction, they will arrive at Wake Island on June 26.
- People traveling westward from the IDL gain one hour every 15° of longitude crossed, while those traveling eastward lose one hour. Therefore, people traveling westwards without adjusting their time back by an hour for every 15° meridian will discover that they have gained an extra day when they return home.
- This happened to Ferdinand Magellan’s crew after their 1522 expedition. However, one loses 24 hours or one day if they travel eastwards around the globe.
- For two hours a day, between 10:00 and 11:59 UTC, there are three separate calendar dates. For example, at 10:30 UTC on Friday, it is 11:30 PM Thursday in American Samoa, 12:30 AM UTC Saturday in Kiritimati and 6:30 AM UTC Friday in New York. Baker Islandand Howland Island have the Earth’s latest time at UTC-12, while Kiritimati (Kiribati) is among the first places to see a new day at UTC +14.
