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Indian Standard Time (IST), sometimes also called India Standard Time, is the time zone 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 ...
, with a time offset 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 (typical ...
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 back ...
.


History

After Independence in 1947, the Union government established IST as the official time for the whole country, although
Kolkata Kolkata (, or , ; also known as Calcutta , List of renamed places in India#West Bengal, the official name until 2001) is the Capital city, capital of the Indian States and union territories of India, state of West Bengal, on the eastern ba ...
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 secon ...
retained their own local time (known as Calcutta Time and Bombay Time) 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 ...
to a location at Shankargarh Fort in Allahabad district, 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.


Calculation

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 and was declared as IST in 1947 for the dominion of India. The longitude of 82°5'E passing through Naini near Allahabad was chosen as the
standard meridian In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle (in degrees or other units) east or west of a given prime meridian (currently, the IERS Reference Meridian). In other words, it is a li ...
for the whole country, because there is a time lag of more than an hour between western India ( around +05:00) and northeastern India ( 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.


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 in the far west. Inhabitants of the
northeastern states The Northeastern United States, also referred to as the Northeast, the East Coast, or the American Northeast, is a geographic region of the United States. It is located on the Atlantic coast of North America, with Canada to its north, the Southe ...
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 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 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." 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 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 The Northeastern United States, also referred to as the Northeast, the East Coast, or the American Northeast, is a geographic region of the United States. It is located on the Atlantic coast of North America, with Canada to its north, the Southe ...
of India. However, the proposal would need to be cleared by the union government. In June 2017,
Department of Science and Technology Department of Science and Technology may refer to: *Department of Science and Technology (Australia), an Australian Government department between November 1980 and December 1984 * Department of Science and Technology (India) * Department of Science ...
(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) and ending on 2 October ( Gandhi Jayanti) was submitted to DST for consideration.


Time signals

Official time signals are generated by the Time and Frequency Standards Laboratory at the National Physical Laboratory in
New Delhi New Delhi (, , ''Naī Dillī'') is the Capital city, capital of India and a part of the NCT Delhi, National Capital Territory of Delhi (NCT). New Delhi is the seat of all three branches of the government of India, hosting the Rashtrapati B ...
, 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 betw ...
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 ...
. 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 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- 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 national All India Radio 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 servers 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 ...
(GPS) receivers.


See also

* Bombay Time * Calcutta Time * Equation of time *
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 * Madras Time * Port Blair mean time * Railway time in India * Sri Lanka Standard Time *
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 India * Time in Sri Lanka * Time zone ( list) * UTC+05:30 *
Zoneinfo 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 ...


References


External links


National Physical Laboratory''Evaluating two timezones ic">''Evaluating two timezones 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