World Library  
Flag as Inappropriate
Email this Article

Indian Standard Time


Indian Standard Time

IST in relation with the bordering nations

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. In military and aviation time IST is designated E* ("Echo-Star").[1]

Indian Standard Time is calculated on the basis of 82.5° E longitude, in Shankargarh Fort () (in Allahabad district in the state of Uttar Pradesh) which is nearly on the corresponding longitude reference line.[2]

In the tz database it is represented by Asia/Kolkata.


  • History 1
  • Criticism and proposals 2
  • Time signals 3
  • See also 4
  • References 5
  • External links 6


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 (known as Calcutta time and Bombay Time) until 1948 and 1955, respectively.[3] The Central observatory was moved from Chennai to a location at Shankar Garh Fort Allahabad District, so that it would be as close to UTC +5:30 as possible.

Daylight Saving Time (DST) was used briefly during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971.[4]

Criticism and proposals

The country's east–west distance of more than 2,933 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 northeastern states have to advance their clocks with the early sunrise and avoid the extra consumption of energy after daylight hours.[5]

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.[5][6]

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.[5] 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."[7]

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.[8] In Assam, tea gardens follow a separate time zone known as the 'Tea Garden Time' or Bagantime that is one hour ahead of IST.[9]

The filmmaker Jahnu Barua has been campaigning for a separate time zone (daylight saving time) for the past 25 years. In 2010, he suggested creating a separate time zone for the Development of Northeastern Region.[10]

In 2014, Chief Minister of Assam Tarun Gogoi started campaigning for another time zone for Assam and other northeastern states of India.[11] However, the proposal would be needed to be cleared by the Central Government of India.

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:

  • High frequency broadcast service operating at 10 MHz under call sign ATA to synchronise 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; and
  • Time and frequency calibrations made with the help of pico– and nanoseconds time interval frequency counters and phase recorders.

IST is taken as the standard time as it passes through almost the centre of India. 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.[12]

See also


  1. ^ "Military and Civilian Time Designations". Greenwich Mean Time (GMT). Retrieved 2006-12-02. 
  2. ^ "Two-timing India".  
  3. ^ "Odds and Ends". Indian Railways Fan Club. Retrieved 2006-11-25. 
  4. ^ "India Time Zones". Greenwich Mean Time (GMT). Retrieved 2006-11-25. 
  5. ^ a b c Sen, Ayanjit (2001-08-21). "India investigates different time zones". BBC News. Retrieved 2006-11-25. 
  6. ^ S. Muthiah (2012-09-24). "A matter of time". The Hindu.  
  7. ^ "Standard Time for Different Regions". Department of Science and Technology. 2004-07-22. Retrieved 2006-11-25. 
  8. ^ "A matter of time". National Resource Centre for Women. Retrieved 2006-11-25. 
  9. ^ Rahul Karmakar (2012-09-24). "Change clock to bagantime". Hindustan Times.  
  10. ^
  11. ^
  12. ^ "Satellites for Navigation". Press Information Bureau, Government of India. Retrieved 2006-11-25. 

External links

  • National Physical Laboratory
  • Evaluating two timezones and Daylight Saving Time for India, by Viral Shah & Vikram Aggarwal.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.