View source for Indian Standard Time

{{short description|Time zone observed in India; UTC+05:30}}
{{For|Irish Standard Time|Time in the Republic of Ireland}}
{{Use dmy dates|date=August 2017}}
{{Use Indian English|date=August 2017}}
{{infobox time zone
| title = Indian Standard Time
| caption = {{legend|#b7ec6d|Indian Standard Time}}
| offset = +05:30
| initials = IST
| dst use = none
| display observance = yes
}}
'''Indian Standard Time''' ('''IST'''), sometimes also called '''India Standard Time''', is the [[time zone]] observed throughout the [[Republic of India]], with a [[time offset]] of [[UTC+05:30]]. India does not observe [[daylight saving time]] or other seasonal adjustments. In [[List of military time zones|military and aviation time]], IST is designated '''E*''' ("Echo-Star").<ref>{{cite web|url= https://greenwichmeantime.com/time/india/|title= Military and Civilian Time Designations|access-date= 2006-12-02|work=[[Greenwich Mean Time]]}}</ref> It is indicated as ''Asia/Kolkata'' in the [[Tz database|IANA time zone database]].

==History==
{{Main|Time in India}}
The Indian Standard Time was adopted on 1 January 1906 during the [[British Raj|British era]] with the phasing out of its precursor [[Madras Time]] (Railway Time),<ref>{{cite web|url=https://www.thehindu.com/news/cities/chennai/Madras-375-When-Madras-clocked-the-time/article60343496.ece |title=When Madras clocked the time |work=The Hindu |last=Menon |first=Nitya |date=22 August 2014 |access-date=1 January 2023 }}</ref> and after [[Indian Independence movement|Independence in 1947]], the [[Union 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.<ref name="Princely states">{{cite web|url=http://www.irfca.org/faq/faq-misc.html |title=Odds and Ends |access-date=2006-11-25 |publisher=Indian Railways Fan Club}}</ref> The Central observatory was moved from [[Chennai]]  to a location at Shankargarh Fort in [[Allahabad district]], so that it would be as close to [[UTC+05:30]] as possible.<ref name="Hans 2018">{{cite news |title=India Standard Time |url=https://www.thehansindia.com/posts/index/Hans-Classroom/2018-04-19/India-Standard-Time/374988 |access-date=27 June 2021 |work=The Hans India |publisher=Hyderabad Media House Limited |date=19 April 2018}}</ref>

Daylight Saving Time (DST) was used briefly during the [[Sino-Indian War|China–India War of 1962]] and the Indo-Pakistani [[Indo-Pakistani War of 1965|Wars of 1965]] and [[Indo-Pakistani War of 1971|1971]].<ref name="timez">{{cite web |url =http://wwp.india-time.com/indian-time-zones.htm |title =India Time Zones |access-date =2006-11-25 |work =Greenwich Mean Time |url-status =dead |archive-url =https://web.archive.org/web/20070519085807/http://wwp.india-time.com/indian-time-zones.htm |archive-date =19 May 2007 |df =dmy-all }}</ref>

===Former timezones===
{| class="wikitable" style="text-align: center; font-size:95%;"
|-
! Time Zone
! UTC
! Period
! Purpose
|-
| [[Bombay Time]]
| [[UTC+04:51]]
| 1884–1955
| Official
|-
| [[Calcutta Time]]
| [[UTC+05:30|UTC+05:53:20]]
| 1884–1948
| Official
|-
| [[Madras Time]]
| [[UTC+05:00|UTC+05:21:14]]
| 1802–1906
| Railways
|-
| [[Port Blair mean time]]
| [[UTC+06:00|UTC+06:10:37]]
| 19th century–1906
| Local
|}

==Calculation==
[[File:IST-Mirzapur.svg|thumb|Location of Mirzapur (near Allahabad) and the 82°30’ E longitude that is used as the reference longitude for IST]]

Indian Standard Time is calculated from the reference longitude of IST at 82°30'E passing near [[Vindhyachal]] of [[Mirzapur district]] in Uttar Pradesh.<ref name="bbc" /> In 1905, the meridian passing east of Allahabad was declared as a standard time zone for [[British India]] and was declared as IST in 1947 for the [[Dominion of India]].<ref>{{cite news |title=September 1, 1947: How Indian Standard Time was introduced in country |url=https://www.timesnownews.com/mirror-now/in-focus/article/september-1-1947-how-indian-standard-time-was-introduced-in-country/806185 |access-date=19 April 2022 |work=www.timesnownews.com |language=en}}</ref> This longitude of 82°30'E was chosen as the [[standard meridian]] for the whole country<ref>{{cite news |title=Indian Standard Time: Lack of Scientific Temper |url=https://timesofindia.indiatimes.com/readersblog/nishant-chandravanshi/indian-standard-time-lack-of-scientific-temper-33370/ |access-date=19 April 2022 |work=[[The Times of India]] Blog |date=10 June 2021 |language=en}}</ref> as it is located centrally between [[western India]] ([[UTC+05:00|local time UTC +05:00]]) and [[northeastern India]] ([[UTC+06:00|local time UTC +06:00]]). Currently, the [[National Physical Laboratory of India]] maintains the Indian Standard Time with the help of the [[Allahabad Observatory]].<ref>{{cite news |title=How Indian Standard Time was introduced in India on September 1, 1947 - Explained |url=https://www.jagranjosh.com/current-affairs/how-indian-standard-time-was-introduced-in-country-on-september-1-1947-explained-1630493926-1 |access-date=19 April 2022 |work=Jagranjosh.com |date=1 September 2021}}</ref>

==Criticism and proposals==
The country's east–west distance of more than {{convert|2,933|km|mi}} covers over 29° of longitude, resulting in the sun rising and setting almost two hours earlier on India's [[Anjaw district|eastern]] border than in the [[Rann of Kutch]] in the far west. Inhabitants of the [[Northeast India|northeastern states]] have to advance their clocks with the early sunrise to avoid the extra consumption of energy after daylight hours.<ref name="bbc">{{cite web |url=http://news.bbc.co.uk/2/hi/south_asia/1501252.stm |title=India investigates different time zones|access-date=2006-11-25 |last=Sen |first=Ayanjit |date=2001-08-21 |work=BBC News}}</ref>

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, but the recommendations were not adopted.<ref name="bbc"/><ref name="thehindu2002">{{cite web|url=http://www.hindu.com/thehindu/mp/2002/01/07/stories/2002010700130300.htm |archive-url=https://web.archive.org/web/20020324174028/http://hindu.com/thehindu/mp/2002/01/07/stories/2002010700130300.htm|url-status=dead|archive-date=2002-03-24|title=A matter of time|access-date=2006-11-25|first=S.|last=Muthiah|date=2012-09-24 |work=[[The Hindu]]}}</ref>

In 2001, the government established a four-member committee under the [[Ministry of Science and Technology (India)|Ministry of Science and Technology]] to examine the need for multiple time zones and daylight saving.<ref name="bbc"/> The findings of the committee, which were presented to [[Parliament of India|Parliament]] in 2004 by the Minister of 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.'<ref>{{cite web |url=http://dst.gov.in/admin_finance/un-sq1007.htm |title=Standard Time for Different Regions |access-date=2006-11-25 |date=2004-07-22 |work=Department of Science and Technology |url-status=dead |archive-url=https://web.archive.org/web/20070928010543/http://dst.gov.in/admin_finance/un-sq1007.htm |archive-date=28 September 2007 |df=dmy-all }}</ref>

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'' allow the union and state governments to define and set the local time for a particular industrial area.<ref>{{cite web |url=http://nrcw.nic.in/shared/sublinkimages/19.htm |title=A matter of time |access-date=2006-11-25 |work=National Resource Centre for Women |url-status=dead |archive-url=https://web.archive.org/web/20060319181936/http://nrcw.nic.in/shared/sublinkimages/19.htm |archive-date=19 March 2006 |df=dmy-all }}</ref> In [[Assam]], tea gardens follow a separate time zone, known as the ''Chaibagan'' or ''Bagan'' time ('Tea Garden Time'), which is one hour ahead of IST.<ref name="HindustanTimes2008">{{cite web |url=http://www.hindustantimes.com/News-Feed/India/Change-clock-to-bagantime/Article1-304181.aspx |title=Change clock to bagantime |access-date=2008-09-22 |last=Rahul Karmakar |date=2012-09-24 |work=[[Hindustan Times]] |url-status=dead |archive-url=https://web.archive.org/web/20110606065730/http://www.hindustantimes.com/News-Feed/india/Change-clock-to-bagantime/Article1-304181.aspx |archive-date=6 June 2011 |df=dmy-all }}</ref>  Still, Indian Standard Time remains the only officially used time.

In 2014, Chief Minister of Assam [[Tarun Gogoi]] started campaigning for another time zone for [[Assam]] and other [[northeast India|northeastern states]] of India.<ref>{{Cite news|url=https://timesofindia.indiatimes.com/india/Gogoi-for-separate-time-zone-for-Assam/articleshow/28252502.cms?referral=PM|title=Gogoi for separate time zone for Assam - Times of India|work=The Times of India|access-date=2018-05-10}}</ref><ref>{{cite web|url=http://www.ndtv.com/article/india/india-could-get-second-time-zone-with-assam-one-hour-ahead-466326?curl=1388743528|title=India could get second time zone with Assam one hour ahead|website=ndtv.com}}</ref> However, the proposal would need to be cleared by the [[Government of India|union government]].

In June 2017, the [[Department of Science and Technology (India)|Department of Science and Technology]] (DST) indicated that it is once again studying the feasibility of two time zones for India. Proposals for creating an additional Eastern India Time (EIT at [[UTC+06:00]]), shifting default IST to [[UTC+05:00]] and daylight saving (Indian Daylight Time for IST and Eastern India Daylight Time for EIT) starting on 14 April ([[Ambedkar Jayanti]]) and ending on 2 October ([[Gandhi Jayanti]]) was submitted to DST for consideration.<ref>{{Cite news|url=http://economictimes.indiatimes.com/news/politics-and-nation/government-assessing-feasibility-of-different-time-zones-in-india/articleshow/59268686.cms|title=Government assessing feasibility of different time zones in India|date=2017-06-22|work=The Economic Times|access-date=2017-08-18}}</ref>{{update inline|date=February 2020}}

==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 clock]]s and synchronised with the worldwide system of clocks that support [[Coordinated Universal Time]].

Features of the Time and Frequency Standards Laboratory include:
*[[High frequency|High-frequency]] broadcast service operating at 10&nbsp;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<sup>−10</sup>.
*Time and frequency calibrations made with the help of [[picosecond|pico-]] and [[nanosecond]]s time interval [[frequency counter]]s and [[phase (waves)|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 national [[All India Radio]] and [[Doordarshan]] television network. Telephone companies have dedicated phone numbers connected to mirror [[time server]]s that also relay the precise time. Another increasingly popular means of obtaining the time is through [[Global Positioning System]] (GPS) receivers.<ref>{{cite web|url=http://pib.nic.in/release/rel_print_page.asp?relid=19703 |title=Satellites for Navigation |access-date=2006-11-25 |work=Press Information Bureau, Government of India}}</ref>

As part of the '''Times Dissemination Project''', which is overseen by the [[Ministry of Consumer Affairs, Food and Public Distribution|Ministry of Consumer Affairs, Food, and Public Distribution]], [[NavIC]] will take the position of GPS as the reference time provider at the National Physical Laboratory from 2025. With an atomic clock in each of the four other centers—[[Ahmedabad]], [[Bengaluru]], [[Bhubaneswar]], and [[Guwahati]]—the reference time from NavIC will be transmitted via an [[optical fiber]] link from the Faridabad center. Indian Standard Time must be used as the exclusive time reference for official, commercial, administrative, and legal documents, according to draft regulations published by the [[Department of Consumer Affairs (India)|Department of Consumer Affairs]]. Exceptions will be permitted for astronomy, navigation, and scientific research.<ref>{{Cite news |date=27 January 2025 |title=Department of Consumer Affairs, Government of India notifies Draft Legal Metrology (Indian Standard Time) Rules, 2025 to Synchronize Time across India |url=https://pib.gov.in/PressReleasePage.aspx?PRID=2096622 |access-date=29 January 2025 |work=[[Press Information Bureau]] |agency=Ministry of Consumer Affairs, Food & Public Distribution, Government of India.}}</ref><ref>{{Cite news |last=Dash |first=Dipak K |date=2025-01-28 |title=Now, India will move to 'one nation, one time', thanks to desi satellites network |url=https://timesofindia.indiatimes.com/india/now-india-will-move-to-one-nation-one-time-thanks-to-desi-satellites-network/articleshow/117615893.cms |access-date=2025-01-29 |work=The Times of India |issn=0971-8257}}</ref>

==See also==
*[[Equation of time]]
*[[International Atomic Time]]
*[[Ist (disambiguation)|Ist]] (disambiguation page)
*[[John Goldingham]]
*[[Railway time#India|Railway time in India]]
*[[Sri Lanka Standard Time]]
*[[Terrestrial Time]]
*[[Time in India]]
*[[Time in Sri Lanka]]
*[[Time zone]] ([[Lists of time zones|list]])
*[[UTC+05:30]]
*[[Zoneinfo]]

==References==
{{Reflist|2}}

==External links==
*[https://worlddatetime.com/time/India Current Time in India]
*[http://www.nplindia.org/ National Physical Laboratory]
*[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.394.7155&rep=rep1&type=pdf ''Evaluating two timezones<nowiki>[sic]</nowiki> and Daylight Saving Time for India''], by Viral Shah & Vikram Aggarwal.
*[https://isttime.com IST Time Now]

{{Asia topic|Time in}}

[[Category:Time in India]]
[[Category:Geography of India|Time]]
[[Category:Time zones]]