Indian Standard Time
Encyclopedia
Time zone
A time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...
observed throughout India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...
, with a time offset
Time offset
The UTC offset is the time offset from Coordinated Universal Time . It is mostly given as hour or hour and minute. Many time zones employ two time offsets, one for standard time and one for daylight saving time...
of UTC+05:30. India does not observe daylight saving time
Daylight saving time
Daylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...
(DST) or other seasonal adjustments, although DST was used briefly during the Sino–Indian War of 1962
Sino-Indian War
The Sino-Indian War , also known as the Sino-Indian Border Conflict , was a war between China and India that occurred in 1962. A disputed Himalayan border was the main pretext for war, but other issues played a role. There had been a series of violent border incidents after the 1959 Tibetan...
and the Indo–Pakistani Wars of 1965
Indo-Pakistani War of 1965
The Indo-Pakistani War of 1965 was a culmination of skirmishes that took place between April 1965 and September 1965 between Pakistan and India. This conflict became known as the Second Kashmir War fought by India and Pakistan over the disputed region of Kashmir, the first having been fought in 1947...
and 1971
Indo-Pakistani War of 1971
The Indo-Pakistani War of 1971 was a military conflict between India and Pakistan. Indian, Bangladeshi and international sources consider the beginning of the war to be Operation Chengiz Khan, Pakistan's December 3, 1971 pre-emptive strike on 11 Indian airbases...
. In military and aviation time, IST is designated E* ("Echo-Star").
Indian Standard Time is calculated on the basis of 82.5° E longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
, from a clock tower in Mirzapur
Mirzapur
Mirzapur is a city in the heart of North India, nearly 650 km between Delhi and Kolkata and also equidistant from Allahabad and Varanasi. Located in the state of Uttar Pradesh, Mirzapur has a population of a little over 205,264 and is renowned for its famous carpet and brassware industry...
(25.15°N 82.58°E) (near Allahabad
Allahabad
Allahabad , or Settled by God in Persian, is a major city of India and is one of the main holy cities of Hinduism. It was renamed by the Mughals from the ancient name of Prayaga , and is by some accounts the second-oldest city in India. It is located in the north Indian state of Uttar Pradesh,...
in the state of Uttar Pradesh
Uttar Pradesh
Uttar Pradesh abbreviation U.P. , is a state located in the northern part of India. With a population of over 200 million people, it is India's most populous state, as well as the world's most populous sub-national entity...
) which is nearly on the corresponding longitude reference line.
In the tz database it is represented by Asia/Kolkata
Asia/Kolkata
Asia/Kolkata is a time zone identifier from the zone file of the tz database. The data is as follows: The reference point is Kolkata....
.
History
After independence in 1947Indian independence movement
The term Indian independence movement encompasses a wide area of political organisations, philosophies, and movements which had the common aim of ending first British East India Company rule, and then British imperial authority, in parts of South Asia...
, the Indian government
Government of India
The Government of India, officially known as the Union Government, and also known as the Central Government, was established by the Constitution of India, and is the governing authority of the union of 28 states and seven union territories, collectively called the Republic of India...
established IST as the official time for the whole country, although Kolkata and Mumbai retained their own local time for a few more years. The Central observatory was moved from Chennai to a location near Mirzapur
Mirzapur
Mirzapur is a city in the heart of North India, nearly 650 km between Delhi and Kolkata and also equidistant from Allahabad and Varanasi. Located in the state of Uttar Pradesh, Mirzapur has a population of a little over 205,264 and is renowned for its famous carpet and brassware industry...
, 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.
Criticism and proposals
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 KutchRann of Kutch
The Great Rann of Kutch, also called Greater Rann of Kutch or just Rann of Kutch , is a seasonal salt marsh located in the Thar Desert in the Kutch District of Gujarat, India and the Sindh province of Pakistan....
in the far west. Inhabitants of the north–eastern states
North-East India
Northeast India refers to the easternmost region of India consisting of the contiguous Seven Sister States, Sikkim, and parts of North Bengal...
have to advance their clocks with the early sunrise and 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
Parliament of India
The Parliament of India is the supreme legislative body in India. Founded in 1919, the Parliament alone possesses legislative supremacy and thereby ultimate power over all political bodies in India. The Parliament of India comprises the President and the two Houses, Lok Sabha and Rajya Sabha...
in 2004 by the Minister for Science and Technology, Kapil Sibal
Kapil Sibal
Kapil Sibal is an Indian politician and lawyer. He is currently the Minister of Communications and Information Technology. He also held the two ministries Ministry of Science and Technology and Ministry of Earth Sciences in the First Manmohan Singh Cabinet...
, 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 do allow the Central and State governments to define and set the local time for a particular industrial area. In Assam, tea gardens follow a separate time zone known as the Tea Garden Time or Bagantime that is one hour ahead of IST.
Time signals
Official time signals are generated by the Time and Frequency Standards LaboratoryTime 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 rubidium atomic clocks...
at the National Physical Laboratory in New Delhi, for both commercial and official use. The signals are based on atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
s and are synchronised with the worldwide system of clocks that support the Coordinated Universal Time
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...
.
Features of the Time and Frequency Standards Laboratory include:
- Four caesiumCaesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
and rubidiumRubidiumRubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
atomic clocks; - High frequencyHigh frequencyHigh frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
broadcast service operating at 10 MHz under call sign ATA to synchronise the user clock within a millisecond; - Indian National Satellite SystemIndian National Satellite SystemINSAT or the Indian National Satellite System is a series of multipurpose Geo-stationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue operations....
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–PicosecondA picosecond is 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years....
and nanosecondNanosecondA nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....
s time interval frequency counterFrequency counterA frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Frequency is defined as the number of events of a particular sort occurring in a set period of time. Frequency counters usually measure the number of oscillations or pulses per second in a...
s and phasePhase (waves)Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...
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
All India Radio
All India Radio , officially known since 1956 as Akashvani , is the radio broadcaster of India and a division of Prasar Bharati. Established in 1936, it is the sister service of Prasar Bharati's Doordarshan, the national television broadcaster. All India Radio is one of the largest radio networks...
and Doordarshan
DoorDarshan
Doordarshan is an Indian public service broadcaster, a division of Prasar Bharati. It is one of the largest broadcasting organizations in India in terms of the infrastructure of studios and transmitters. Recently, it has also started Digital Terrestrial Transmitters. On September 15, 2009,...
television network. Telephone companies have dedicated phone numbers connected to mirror
Mirror (computing)
In computing, a mirror is an exact copy of a data set. On the Internet, a mirror site is an exact copy of another Internet site.Mirror sites are most commonly used to provide multiple sources of the same information, and are of particular value as a way of providing reliable access to large downloads...
timeserver
Timeserver
A time server is a server computer that reads the actual time from a reference clock and distributes this information to its clients using a computer network...
s that also relay the precise time. Another increasingly popular means of obtaining the time is through Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) receivers.
See also
- Equation of timeEquation of timeThe equation of time is the difference between apparent solar time and mean solar time. At any given instant, this difference will be the same for every observer...
- International Atomic TimeInternational Atomic TimeInternational Atomic Time is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid...
- Terrestrial TimeTerrestrial TimeTerrestrial Time is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of the Earth....
- Time zoneTime zoneA time zone is a region on Earth that has a uniform standard time for legal, commercial, and social purposes. In order for the same clock time to always correspond to the same portion of the day as the Earth rotates , different places on the Earth need to have different clock times...
(list) - ZoneinfoZoneinfoThe tz database, also called the zoneinfo database or IANA Time Zone Database, is a collaborative compilation of information about the world's time zones, primarily intended for use with computer programs and operating systems. It is sometimes referred to as the Olson database after the founding...
External links
- National Physical Laboratory
- Evaluating two timezones and Daylight Saving Time for India, by Viral Shah & Vikram Aggarwal.