Indian Standard Time (IST), sometimes also called India Standard Time, is the
time zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
observed throughout
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, with a
time offset
The UTC offset is the difference in hours and minutes between Coordinated Universal Time (UTC) and local solar time, at a particular place. This difference is expressed with respect to UTC and is generally shown in the format , , or . So if the tim ...
of
UTC+05:30. India does not observe
daylight saving time
Daylight saving time (DST), also referred to as daylight savings time or simply daylight time (United States, Canada, and Australia), and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks (typicall ...
or other seasonal adjustments. In
military and aviation time, IST is designated E* ("Echo-Star"). It is indicated as Asia/Kolkata in the
IANA time zone database
The tz database is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. Paul Eggert is its current editor and maintainer, with the organizational backi ...
.
History
After
Independence in 1947, the
Union government
The Government of India ( ISO: ; often abbreviated as GoI), known as the Union Government or Central Government but often simply as the Centre, is the national government of the Republic of India, a federal democracy located in South Asia, ...
established IST as the official time for the whole country, although
Kolkata
Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, comme ...
and
Mumbai
Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the second- ...
retained their own local time (known as
Calcutta Time
Calcutta time was one of the two time zones established in British India in 1884. It was established during the International Meridian Conference held at Washington, D.C. in the United States. It was decided that India had two time zones: Calcu ...
and
Bombay Time
Bombay Time was one of the two official time zones established in British India in 1884. The time zone was established during the International Meridian Conference held at Washington, D.C. in the United States in 1884. It was then decided that I ...
) until 1948 and 1955, respectively.
The Central observatory was moved from
Chennai
Chennai (, ), formerly known as Madras ( the official name until 1996), is the capital city of Tamil Nadu, the southernmost Indian state. The largest city of the state in area and population, Chennai is located on the Coromandel Coast of th ...
to a location at Shankargarh Fort in
Allahabad district
Allahabad district, officially known as Prayagraj district, is the most populous district of Uttar Pradesh state of India. The district headquarters is Allahabad which was renamed Prayagraj at the same time as the district was renamed. The Di ...
, so that it would be as close to
UTC+05:30 as possible.
Daylight Saving Time (DST) was used briefly during the
China–India War of 1962 and the Indo-Pakistani
Wars of 1965 and
1971 *
The year 1971 had three partial solar eclipses ( February 25, July 22 and August 20) and two total lunar eclipses (February 10, and August 6).
The world population increased by 2.1% this year, the highest increase in history.
Events
Ja ...
.
Calculation
![IST-Mirzapur](https://upload.wikimedia.org/wikipedia/commons/5/57/IST-Mirzapur.svg)
Indian Standard Time is calculated from
the clock tower in Mirzapur nearly exactly on the reference longitude of IST at 82°30'E, within 4 angular minutes.
In 1905, the meridian passing east of Allahabad was declared as a standard time zone for
British India
The provinces of India, earlier presidencies of British India and still earlier, presidency towns, were the administrative divisions of British governance on the Indian subcontinent. Collectively, they have been called British India. In one ...
and was declared as IST in 1947 for the
dominion of India
The Dominion of India, officially the Union of India,* Quote: “The first collective use (of the word "dominion") occurred at the Colonial Conference (April to May 1907) when the title was conferred upon Canada and Australia. New Zealand and N ...
. The longitude of 82°5'E passing through Naini near
Allahabad
Allahabad (), officially known as Prayagraj, also known as Ilahabad, is a metropolis in the Indian state of Uttar Pradesh.The other five cities were: Agra, Kanpur (Cawnpore), Lucknow, Meerut, and Varanasi (Benares). It is the administrat ...
was chosen as the
standard meridian for the whole country, because there is a time lag of more than an hour between
western India
Western India is a loosely defined region of India consisting of its western part. The Ministry of Home Affairs in its Western Zonal Council Administrative division includes the states of Goa, Gujarat, and Maharashtra along with the Union te ...
(
around +05:00) and
northeastern India
, native_name_lang = mni
, settlement_type =
, image_skyline =
, image_alt =
, image_caption =
, motto =
, image_map = Northeast india.png
, ...
(
around +06:00), hence approximately standardizing with
UTC+05:30 of
central India. Currently, the
Council of Scientific and Industrial Research- National Physical Laboratory (CSIR-NPL) maintains the Indian Standard Time with the help of the
Allahabad Observatory
The Allahabad Observatory located in the suburb of Jhusi, just outside Allahabad is the centre responsible for maintaining the Indian Standard Time. The observatory is located at 82.5°E longitude, which translates to an exact time difference ...
.
Criticism and proposals
The country's east–west distance of more than covers over 29 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
The Rann of Kutch (alternately spelled as Kuchchh) is a large area of salt marshes that span the border between India and Pakistan. It is located in Gujarat (primarily the Kutch district), India, and in Sindh, Pakistan. It is divided into t ...
in the far west. Inhabitants of the
northeastern states have to advance their clocks with the early sunrise to 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.
In 2001, the government established a four-member committee under the
Ministry of Science and Technology A Science Ministry or Department of Science is a ministry or other government agency charged with science. The ministry is often headed by a Minister for Science.
List of Ministries of Science
Many countries have a Ministry of Science or Ministry ...
to examine the need for multiple time zones and daylight saving.
The findings of the committee, which were presented to
Parliament
In modern politics, and history, a parliament is a legislative body of government. Generally, a modern parliament has three functions: Representation (politics), representing the Election#Suffrage, electorate, making laws, and overseeing ...
in 2004 by the Minister of Science and Technology,
Kapil Sibal
Kapil Sibal (born 8 August 1948) is an Indian lawyer and politician. Sibal has represented several high-profile cases in the Supreme Court of India and is widely regarded as one of the famous lawyers of India. He is a Member of Parliament, in Ra ...
, 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."
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. In
Assam
Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
, tea gardens follow a separate time zone, known as the ''Chaibagan'' or ''Bagan'' time ('Tea Garden Time'), which is one hour ahead of IST.
Still Indian Standard Time remains the only officially used time.
In 2014, Chief Minister of Assam
Tarun Gogoi
Tarun Gogoi (11 October 1936 – 23 November 2020) was an Indian politician who served as the Chief Minister of Assam from 2001 to 2016. He was a member of the Indian National Congress and led the party to a record three consecutive electoral vi ...
started campaigning for another time zone for
Assam
Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
and other
northeastern states of India. However, the proposal would need to be cleared by the
union government
The Government of India ( ISO: ; often abbreviated as GoI), known as the Union Government or Central Government but often simply as the Centre, is the national government of the Republic of India, a federal democracy located in South Asia, ...
.
In June 2017,
Department of Science and Technology (DST) indicated that they are once again studying 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
Ambedkar Jayanti or Bhim Jayanti is an annual festival observed on 14 April to commemorate the memory of B. R. Ambedkar, Indian politician and civil rights activist. It marks Dr. Babasaheb Ambedkar's birthday who was born on 14 April 1891. Si ...
) and ending on 2 October (
Gandhi Jayanti
Gandhi Jayanti is an event celebrated in India to mark the birthday of Mahatma Gandhi. It is celebrated annually on 2 October, and is one of the three national holidays of India. The UN General Assembly announced on 15 June 2007 that it adop ...
) was submitted to DST for consideration.
Time signals
Official time signals are generated by the
Time and Frequency Standards Laboratory
The Time and Frequency Standards Laboratory is a part of the National Physical Laboratory in New Delhi which maintains and calibrates the Indian Standard Time.
Features of the Time and Frequency Standards Lab include:
* Four caesium and rubidi ...
at the National Physical Laboratory in
New Delhi
New Delhi (, , ''Naī Dillī'') is the capital of India and a part of the National Capital Territory of Delhi (NCT). New Delhi is the seat of all three branches of the government of India, hosting the Rashtrapati Bhavan, Parliament House ...
, for both commercial and official use. The signals are based on
atomic clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...
s and are synchronised with the worldwide system of clocks that support the
Coordinated Universal Time
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used ...
.
Features of the Time and Frequency Standards Laboratory include:
*
High frequency
High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...
broadcast service operating at 10 MHz under call sign ''ATA'' to synchronise the user clock within a millisecond;
*
Indian National Satellite System
The Indian National Satellite System or INSAT, is a series of multipurpose geostationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue operations. Commissioned in 1983, INSAT i ...
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-
A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The pre ...
and
nanosecond
A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds.
The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...
s time interval
frequency counter
A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Frequency counters usually measure the number of cycles of oscillation, or pulses per second in a periodic electronic signal. Such an instr ...
s and
phase
Phase or phases may refer to:
Science
*State of matter, or phase, one of the distinct forms in which matter can exist
*Phase (matter), a region of space throughout which all physical properties are essentially uniform
* Phase space, a mathematic ...
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
All or ALL may refer to:
Language
* All, an indefinite pronoun in English
* All, one of the English determiners
* Allar language (ISO 639-3 code)
* Allative case (abbreviated ALL)
Music
* All (band), an American punk rock band
* ''All'' (All a ...
and
Doordarshan
Doordarshan (abbreviated as DD; Hindi: , ) is an Indian public service broadcaster founded by the Government of India, owned by the Ministry of Information and Broadcasting and one of Prasar Bharati's two divisions. One of India's largest bro ...
television network. Telephone companies have dedicated phone numbers connected to mirror
time server
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...
s that also relay the precise time. Another increasingly popular means of obtaining the time is through
Global Positioning System
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
(GPS) receivers.
See also
*
Bombay Time
Bombay Time was one of the two official time zones established in British India in 1884. The time zone was established during the International Meridian Conference held at Washington, D.C. in the United States in 1884. It was then decided that I ...
*
Calcutta Time
Calcutta time was one of the two time zones established in British India in 1884. It was established during the International Meridian Conference held at Washington, D.C. in the United States. It was decided that India had two time zones: Calcu ...
*
Equation of time
In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in ...
*
International Atomic Time
International Atomic Time (abbreviated TAI, from its French name ) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid. TAI is a weighted average of the time kept by over 450 ato ...
*
John Goldingham
John Goldingham FRS (1767 - July 1849) was the first official astronomer of the Madras Observatory, appointed in 1802. Goldingham was also an architect and surveyor who headed the Madras Survey School which later grew into the Guindy Engineering ...
*
Madras Time
Madras Time was a time zone established in 1802 by John Goldingham, the first official astronomer of the British East India Company in India when he determined the longitude of Madras as 5 hours, 21 minutes and 14 seconds ahead of Greenwich Mean ...
*
Port Blair mean time
Port Blair mean time was the time zone of the Andaman and Nicobar Islands of India in the Bay of Bengal. The time zone was set up during the early 19th century and has been described as 17 minutes and 17 seconds (UTC+6:10:37) ahead of the Calcut ...
*
Railway time in India
*
Sri Lanka Standard Time
Sri Lanka Standard Time (SLST) ( si, ශ්රී ලංකාවේ සම්මත වේලාව , Shri Lankavay Sammatha Velava, ta, இலங்கை நியம நேரம்) is the time zone for Sri Lanka. It is 5 hours and 30 ...
*
Terrestrial Time
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth.
For example, the Astronomical Almanac uses T ...
*
Time in Afghanistan
Time in Afghanistan is officially UTC+04:30, called Afghanistan Time or AFT. Afghanistan does not observe daylight saving time.
IANA time zone database
Afghanistan has the IANA time zone database
The tz database is a collaborative compila ...
*
Time in India
The Republic of India uses only one time zone (even though it spans across two geographical time zones) across the whole nation and all its territories, called Indian Standard Time (IST), which equates to UTC+05:30, i.e. five and a half hours a ...
*
Time in Sri Lanka Time in Sri Lanka since is officially represented by the Sri Lanka Standard Time (SLST, UTC+05:30).
Historic UTC offsets were:
* UTC+05:30
* UTC+06:00
* UTC+06:30
Daylight saving time
In history daylight saving time was used too. IANA time zo ...
*
Time zone
A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...
(
list
A ''list'' is any set of items in a row. List or lists may also refer to:
People
* List (surname)
Organizations
* List College, an undergraduate division of the Jewish Theological Seminary of America
* SC Germania List, German rugby union ...
)
*
UTC+05:30
*
Zoneinfo
References
External links
National Physical Laboratory''Evaluating_two_timezones[sic/nowiki>_and_Daylight_Saving_Time_for_India''.html" ;"title="ic">''Evaluating two timezones
ic">''Evaluating_two_timezones[sic
/nowiki>_and_Daylight_Saving_Time_for_India''_by_Viral_Shah_&_Vikram_Aggarwal.
{{Asia_topic.html" ;"title="ic
/nowiki> and Daylight Saving Time for India''">ic">''Evaluating two timezones Time_in
Time_in_India
Geography_of_India.html" ;"title="ic
/nowiki> and Daylight Saving Time for India'' by Viral Shah & Vikram Aggarwal.
{{Asia topic">Time in
Time in India
Geography of India">ic
/nowiki> and Daylight Saving Time for India'' by Viral Shah & Vikram Aggarwal.
{{Asia topic">Time in
Time in India
Geography of India
Time zones