The Full Wiki

Indian Standard Time: Wikis


Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.


From Wikipedia, the free encyclopedia

Indian Standard Time (IST) is the time observed throughout India and Sri Lanka, with a time offset of UTC+05:30. 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.[1] In military and aviation time, IST is designated E* ("Echo-Star").[2]

Indian Standard Time is calculated on the basis of 82.5° E longitude, which is just west of the town of Mirzapur, near Allahabad in the state of Uttar Pradesh.[3]

In his writing, Salman Rushdie notes that an analog clock following Greenwich Mean Time displays Indian Standard Time when turned upside down.



One of the earliest descriptions of standard time in India appeared in the 4th century CE astronomical treatise Surya Siddhana. 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 (23°10′58″N 75°46′38″E / 23.18278°N 75.77722°E / 23.18278; 75.77722 (Avanti (Ujjain))), and Rohitaka, the ancient name for Rohtak (28°54′N 76°38′E / 28.9°N 76.633°E / 28.9; 76.633 (Rohitaka (Rohtak))), a city near the historic battle-field of Kurukshetra.[4]

Situated upon the line which passes through the haunt of the demons (equator and 76° E) and the mountain which is the seat of the gods (the North Pole), are Rohitaka and Avanti ...[5]

The day used by ancient Indian astronomers began at sunrise at the prime meridian of Ujjain,[6] and was divided into smaller time units in the following manner:[7]

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 prāṇas. The ghalikā is 60 palas, and the nakṣatra ahórātra, or astronomical day, contains 60 ghalikās. A 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.[8] The Surya Siddhanta also described a method of converting local time to the standard time of Ujjain.[5] 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 calendar in both lunar and solar units.[9] For example, the Jantar Mantar observatory built by Maharaja Sawai Jai Singh in Jaipur in 1733 contains large sundials, up to 90 ft (27 m) high, which were used to accurately determine the local time.


Time under British rule in India

In 1802 Madras time was setup by John Goldingham and this was used widely by the railways in India.[citation needed] Though 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.[10]

IST in relation with the bordering nations

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.[10]

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.[10] 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.

During the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971, daylight saving was briefly used to reduce civilian energy consumption.

Time zones

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 cycle[citation needed]. 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 Kutch in 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.[11]

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.[11][12]

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.[11] 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."[13]

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.[14] In Assam, tea gardens follow a separate time zone known as the Tea Garden Time or Bagantime that is one hour ahead of IST[15].

Time signals

Official time signals are generated by the Time and Frequency Standards Laboratory at 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:[16]

To communicate the exact time to the people, the exact time is broadcast over the state–owned All India Radio and Doordarshan television 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.[17]

See also


  1. ^ "India Time Zones". Greenwich Mean Time (GMT). Retrieved 2006-11-25. 
  2. ^ "Military and Civilian Time Designations". Greenwich Mean Time (GMT). Retrieved 2006-12-02. 
  3. ^ |title=Two-timing India|date=2007-09-04|work=Hindustan Times|accessdate=2008-08-29}}
  4. ^ Schmidt, Olaf H. (1944). "The Computation of the Length of Daylight in Hindu Astronomy". Isis, 35(3):205–211. The University of Chicago Press. Retrieved 2006-11-29. 
  5. ^ a b Burgess, Ebenezer. 1858–1860. "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).
  6. ^ Swerdlow, N. 1973. "A Lost Monument of Indian Astronomy." Isis. 64(2):239–243.
  7. ^ Das, Sukumar Ranjan. 1928. "The Equation of Time in Hindu Astronomy">, The American Mathematical Monthly, 35(10):540–543. Retrieved 1 December 2006.
  8. ^ Piepoli, M. 1997. "Origin of Respiratory Sinus Arrhythmia in Conscious Humans." Circulation. 95:1813–1821. Retrieved 1 December 2006.
  9. ^ Tomczak, Matthias (2004-07-15). "Lecture 7: Living with the seasons—the calendar problem". Lectures on Science, civilization and society, Flinders University, Australia. Retrieved 2006-12-01. 
  10. ^ a b c "Odds and Ends". Indian Railways Fan Club. Retrieved 2006-11-25. 
  11. ^ a b c Sen, Ayanjit (2001-08-21). "India investigates different time zones". BBC News. Retrieved 2006-11-25. 
  12. ^ S. Muthiah (2002-01-07). "A matter of time". The Hindu Business Line. The Hindu Group. Retrieved 2006-11-25. 
  13. ^ "Standard Time for Different Regions". Department of Science and Technology]. 2004-07-22. Retrieved 2006-11-25. 
  14. ^ "A matter of time". National Resource Centre for Women. Retrieved 2006-11-25. 
  15. ^ Rahul Karmakar (2008-04-13). "Change clock to bagantime". Hindustan Times. HT Media Group. Retrieved 2008-09-22. 
  16. ^ "Indian Time Today (IST)". Greenwich Mean Time (GMT). Retrieved 2006-11-25. 
  17. ^ "Satellites for Navigation". Press Information Bureau, Government of India. Retrieved 2006-11-25. 

External links

Simple English

Indian Standard Time (IST) is the time zone for India and Sri Lanka.

Indian Standard Time is 5.5 hours (5 hours 30 minutes) ahead of Greenwich Mean Time(GMT+5.5).


Other websites


Got something to say? Make a comment.
Your name
Your email address