- Indian Standard Time
Indian Standard Time (IST) is the time observed throughout
Indiaand Sri Lanka, with a time offsetof . India does not observe daylight saving time, (DST) or other seasonal adjustments, although DST was used briefly during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971.cite web | url =http://wwp.india-time.com/indian-time-zones.htm | title =India Time Zones | accessdate =2006-11-25|work= [http://wwp.greenwichmeantime.com Greenwich Mean Time (GMT)] ] In military and aviation time, IST is designated E* ("Echo-Star"). [cite web | url = http://wwp.greenwichmeantime.com/info/timezone.htm
title = Military and Civilian Time Designations | accessdate =2006-12-02| work= [http://wwp.greenwichmeantime.com Greenwich Mean Time (GMT)] ]
Indian Standard Time is calculated on the basis of 82.5° E
longitude, which is just west of the town of Mirzapur, near Allahabadin the state of Uttar Pradesh.cite web|url=http://www.hindustantimes.in/StoryPage/Print.aspx?Id=7ae0f1f1-23fd-4e46-98f2-3e0933e87f9f
Hindustan Times|accessdate=2008-08-29] The longitude difference between Mirzapurand the United Kingdom's Royal Observatory at Greenwichtranslates to an exact time difference of 5 hours 30 minutes. Local time is calculated from a clock towerat the Allahabad Observatory(coord|25.15|N|82.5|E|) though the official time-keeping devices are entrusted to the National Physical Laboratory, in New Delhi.cite web | url=http://news.bbc.co.uk/2/hi/south_asia/1501252.stm |title=India investigates different time zones|accessdate=2006-11-25 |last=Sen |first=Ayanjit |date= 2001-08-21|work= [http://news.bbc.co.uk BBC News] ]
One of the earliest descriptions of "standard time" in India appeared in the 4th century CE astronomical treatise
Surya Siddhanta. Postulating a spherical earth, the book defined the prime meridian, or zero longitude, as passing through "Avanti", the ancient name for the historic city of Ujjain(coord|23|10|58|N|75|46|38|E), and "Rohitaka", the ancient name for Rohtak(coord|28|54|N|76|38|E), a city near the historic battle-field of Kurukshetra. [cite web| url=http://www.jstor.org/view/00211753/ap020353/02a00020/0| title=The Computation of the Length of Daylight in Hindu Astronomy| accessdate=2006-11-29| last=Schmidt| first=Olaf H.|year=1944| work= Isis, 35(3):205–211| publisher=The University of Chicago Press]
Situated upon the line which passes through the haunt of the demons (
equatorand 76° E) and the mountain which is the seat of the gods (the North Pole), are Rohitaka and Avanti ...Burgess, Ebenezer. 1858–1860. [http://www.jstor.org/view/00030279/ap020003/02a00030/0 "Translation of the Surya-Sikddhanta, A Text-Book of Hindu Astronomy; With Notes, and an Appendix."] "Journal of the American Oriental Society", 6:141–498. (pages 183–186).]
The day used by ancient Indian astronomers began at sunrise at the prime meridian of Ujjain, [ Swerdlow, N. 1973. [http://www.jstor.org/view/00211753/ap010172/01a00100/0 "A Lost Monument of Indian Astronomy."] "Isis". 64(2):239–243.] and was divided into smaller time units in the following manner: [ Das, Sukumar Ranjan. 1928. [http://www.jstor.org/view/00029890/di991110/99p1463g/0 "The Equation of Time in Hindu Astronomy">, "The American Mathematical Monthly"] , 35(10):540–543. Retrieved 1 December 2006.]
Time that is measurable is that which is in common use, beginning with the "prāṇa" (or, the time span of one breath). The "pala" contains six "Unicode|prāṇas". The "ghalikā" is 60 "palas", and the "Unicode|nakṣatra ahórātra", or astronomical day, contains 60 "ghalikās". A "Unicode|nakṣatra māsa", or astronomical month, consists of 30 days.
Taking a day to be 24 hours, the smallest time unit, "prāṇa", or one respiratory cycle, equals 4 seconds, a value consistent with the "normal breathing frequency" of 15 breaths/min used in modern medical research. [Piepoli, M. 1997. [http://circ.ahajournals.org/cgi/content/full/95/7/1813 "Origin of Respiratory Sinus Arrhythmia in Conscious Humans."] "Circulation". 95:1813–1821. Retrieved 1 December 2006.] The Surya Siddhanta also described a method of converting local time to the standard time of Ujjain. Despite these early advances, standard time was not widely used outside astronomy. For most of India's history, ruling kingdoms kept their own local time, typically using the
Hindu calendarin both lunar and solar units. [cite web|url=http://www.es.flinders.edu.au/~mattom/science+society/lecture7.html| title=Lecture 7: Living with the seasons—the calendar problem|accessdate=2006-12-01| last=Tomczak| first=Matthias|date=2004-07-15 |publisher=Lectures on Science, civilization and society, Flinders University, Australia] For example, the Jantar Mantar observatory built by Maharaja Sawai Jai Singh in Jaipurin 1733 contains large sundials, up to 90 ft (27 m) high, which were used to accurately determine the local time.
In 1792, the
British East India Companyestablished the Madras Observatoryin Chennai(then Madras), largely due to the efforts of the British sailor–astronomer Michael Topping. In 1802, John Goldingham, appointed as the first official astronomer of the Company in India, established the longitude of Madras (coord|13|5|24|N|80|18|30|E|) as 5 hours 30 minutes ahead of Greenwich Mean Timeas the local standard time. This marked the first use of the current time zone, and departure from the earlier standard of the day beginning at sunrise; now it started at midnight. The clock in the observatory was attached to a gun that was fired at 8 p.m. daily to announce that "all was well" with IST. [cite web|url=http://wwp.greenwichmeantime.com/time-zone/asia/india/time/history-indian-time.htm |title=History of Indian Time (IST) |accessdate=2006-11-25 |work= [http://wwp.greenwichmeantime.com/ Greenwich Mean Time (GMT)] ] Time-keeping support for shipping activities in Bombay Harbour was provided by the Colaba Observatory in Bombay, which was established in 1826. [cite web|url=http://iigs.iigm.res.in/history.htm |title=History of Indian Institute of Geomagnetism|accessdate=2006-11-25|date=2006-10-10|publisher= National Informatics Centre]
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, and was gradually adopted by the nearby provinces and princely states. In the 19th century, clocks were kept in synchronisation through by telegraph– for example the railways synchronised their clocks thorough a time signal that was sent from the head office or the regional headquarters at a specified time every day.cite web|url=http://www.irfca.org/faq/faq-misc.html |title=Odds and Ends |accessdate=2006-11-25 |work= [http://www.irfca.org Indian Railways Fan Club] ]
In 1884, the
International Meridian Conferencein Washington, D.C.set up uniform time zones across the world. It was decided that India would have two time zones, with Calcutta using the 90th east meridian and Bombay the 75° E meridian. Calcutta timewas set at 5 hours 30 minutes 21 seconds ahead of GMT, while Bombay timewas 4 hours 51 minutes ahead. [cite web|url=http://www.gutenberg.org/files/17759/17759-h/17759-h.htm |title=Indian Time Zones (IST) |accessdate=2006-11-25 |work= [http://www.gutenberg.org/ Project Gutenberg] | publisher=International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884 Protocols of the Proceedings] By the late 1880s, many railway companies began to use Madras time(known as "Railway time") as an intermediate time between the two zones. Another time zone, Port Blair mean time, was established at Port Blair, the capital of the Andaman and Nicobar Islandsin the Bay of Bengal. The Port Blair mean time was set to 49 minutes 51 seconds ahead of Madras time. [cite web|url=http://cires.colorado.edu/~bilham/Oldham1881account.htm |title=Note on the earthquake of 31 December 1881, Records of the Geological Survey of India,, XVII(2), 47–53, 1884 |accessdate=2006-11-25 |work=Cooperative Institute for Research in Environmental Sciences (CIRES)]
British India did not officially adopt the standard time zones until 1905, when the meridian passing east of Allahabad at 82.5° E longitude was picked as the central meridian for India, corresponding to a single time zone for the country. This came into force on 1 January 1906, and also applied to
Sri Lanka(then Ceylon). However, Calcutta time was officially maintained as a separate time zone until 1948.
In 1925, time synchronisation began to be relayed through omnibus telephone systems and control circuits to organisations that needed to know the precise time. This continued until the 1940s, when time signals began to be broadcast using the radio by the government.
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 was moved from Chennai to a location near
Mirzapur, so that it would be as close to UTC +5:30 as possible.
A single, large time zone has been shown to cost more, and requires rescheduling of events to make them compatible with the rest of the zone or with the day's cycleFact|date=July 2008. The country's east–west distance of more than 2,000 km (1,200 mi) covers over 28 degrees of longitude, resulting in the sun rising and setting almost two hours earlier on India's eastern border than in the
Rann of Kutchin the far west. Inhabitants of the north–eastern states have to advance their clocks with the early sunrise and avoid the extra consumption of energy after daylight hours.
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 recommendations were not adopted.cite web|url=http://www.hinduonnet.com/mp/2002/01/07/stories/2002010700130300.htm |title=A matter of time |accessdate=2006-11-25 |last=S. Muthiah |date=
2002-01-07|work= [http://www.thehindubusinessline.com The Hindu Business Line] |publisher= The HinduGroup]
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, which were presented to Parliament in 2004 by the Minister for Science and Technology,
Kapil Sibal, did not recommend changes to the 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." [cite web|url=http://dst.gov.in/admin_finance/un-sq1007.htm |title=Standard Time for Different Regions |accessdate=2006-11-25 |date= 2004-07-22|work=Department of Science and Technology] ]
Though the government has consistently refused to split the country into multiple time zones, provisions in labour laws such as the "Plantations Labour Act, 1951" do allow the Central and State governments to define and set the local time for a particular industrial area. [cite web|url=http://nrcw.nic.in/shared/sublinkimages/19.htm |title=A matter of time |accessdate=2006-11-25 |work=National Resource Centre for Women] In Assam, tea gardens follow a separate time zone known as the Tea Garden Time or Bagantime that is one hour ahead of ISTcite web|url=http://www.hindustantimes.com/StoryPage/StoryPage.aspx?id=971215e0-8512-4ce2-805d-02592f3aab16 |title= Change clock to bagantime |accessdate=2008-09-22 |last=Rahul Karmakar |date=
2008-04-13|work= [http://www.hindustantimes.com Hindustan Times] |publisher= HT MediaGroup] .
Recently there had been suggestion to advance the Indian Standard Time by half-an-hour.
Official time signals are generated by the
Time and Frequency Standards Laboratoryat the National Physical Laboratory in New Delhi, for both commercial and official use. The signals are based on atomic clocks and are synchronised with the worldwide system of clocks that support the Coordinated Universal Time.
Features of the Time and Frequency Standards Laboratory include: [cite web|url=http://wwp.greenwichmeantime.com/time-zone/asia/india/time/indian-time-today.htm |title=Indian Time Today (IST) |accessdate=2006-11-25 |work= [http://wwp.greenwichmeantime.com/ Greenwich Mean Time (GMT)] |]
caesiumand rubidiumatomic clocks;
High frequencybroadcast service operating at 10 MHz under call sign "ATA" to synchronise the user clock within a millisecond;
Indian National Satellite Systemsatellite–based standard time and frequency broadcast service, which offers IST correct to ±10 microsecond and frequency calibration of up to ±10−10; and
*Time and frequency calibrations made with the help of pico– and
nanoseconds time interval frequency counters and phase recorders.
To communicate the exact time to the people, the exact time is broadcast over the state–owned
All India Radioand Doordarshantelevision network. Telephone companies have dedicated phone numbers connected to mirror timeservers that also relay the precise time. Another increasingly popular means of obtaining the time is through Global Positioning System(GPS) receivers. [cite web|url=http://pib.nic.in/release/rel_print_page.asp?relid=19703 |title=Satellites for Navigation |accessdate=2006-11-25 |work= [http://pib.nic.in Press Information Bureau, Government of India] |]
Equation of time
International Atomic Time
* [http://www.nplindia.ernet.in/time.php National Physical Laboratory]
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