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Indian Standard Time

2007 Schools Wikipedia Selection. Related subjects: Geography of Asia

   Location of Mirzapur and the 82.5° E longitude that is used as the
   reference longitude for Indian Standard Time.
   Enlarge
   Location of Mirzapur and the 82.5° E longitude that is used as the
   reference longitude for Indian Standard Time.

   Indian Standard Time (IST) is the time observed throughout India, with
   a time offset of UTC+5:30. India does not observe daylight saving time
   (DST) or other seasonal adjustments, although DST was used briefly
   during the Sino–Indian War of 1962, and the Indo–Pakistani Wars of 1965
   and of 1971. In military and aviation time, IST is designated E* =
   Echo*.

   Indian Standard Time is calculated on the basis of 82.5 °E longitude
   which is just west of the town of Mirzapur, near Allahabad in the state
   of Uttar Pradesh. The longitude difference between Mirzapur and the
   United Kingdom's Royal Observatory at Greenwich translates to an exact
   time difference of 5 hours and 30 minutes. Local time is calculated
   from a clock tower at the Allahabad Observatory ( 25.15° N 82.5° E)
   though the official time-keeping devices are entrusted to the National
   Physical Laboratory, located in New Delhi.

History

   One of the earliest descriptions of standard time in India appeared in
   the 4th century CE astronomical treatise Surya Siddhanta. Postulating a
   spherical earth, the book defined the prime meridian, or zero
   longitude, as passing through Avanti, the ancient name for the historic
   city of Ujjain ( 23°11′N 75°45′E), and Rohitaka, the ancient name for
   Rohtak ( 28°54′N 76°38′E), a city near the historic battle-field of
   Kurukshetra.

     Situated upon the line which passes through the haunt of the demons
     (equator and 76° E) and the mountain which is the seat of the gods
     (the North Pole), are Rohitaka and Avanti ...

   The sidereal day of ancient Indian astronomy began at sunrise at the
   prime meridian of Ujjain, and was divided into smaller time units in
   the following manner:

     Time that is measurable is that which is in common use, beginning
     with the prāṇa (or, the time span of one breath). The pala contains
     six prāṇas. The ghalikā is 60 palas, and the nakṣatra ahórātra, or
     sidereal day, contains 60 ghalikās. A nakṣatra māsa, or sidereal
     month, consists of 30 sidereal days.

   Taking a sidereal day to be 24 hours, it is easily computed that the
   smallest time unit, prāṇa, or one respiratory cycle, equals 4 seconds,
   a value consistent with the normal breathing frequency of 15
   breaths/min used in modern medical research. The Surya Siddhanta also
   described a method of converting the local time of an observer to the
   standard time of Ujjain. However, despite these early advances,
   standard time was not widely used outside of astronomy. For most of
   India's history, ruling kingdoms kept their own local time, typically
   using the Hindu calendar in both lunar and solar units. For example,
   the Jantar Mantar observatory built by Maharaja Sawai Jai Singh in
   Jaipur in 1733 contains large sundials, up to 90 ft. high, which were
   used to accurately determine the local time.
   Astronomer John Goldingham is credited with the establishment of the
   current fractional time zone (UTC+5:30).
   Enlarge
   Astronomer John Goldingham is credited with the establishment of the
   current fractional time zone (UTC+5:30).

   In 1792, the British East India Company established the Madras
   Observatory in Chennai (then Madras), largely due to the efforts of the
   British sailor–astronomer Michael Topping. In 1802, John Goldingham,
   appointed as the first official astronomer of the Company in India,
   established the longitude of Madras ( 13°5′24″N, 80°18′30″E) as 5 hours
   and 30 minutes ahead of Greenwich Mean Time as the local standard time.
   This marked the first ever use of the current time zone, and departure
   from the earlier standard of the day beginning at sunrise; now it
   started at midnight. The clock in the observatory was attached to a gun
   that was fired at 8 p.m. daily to announce that "all was well" with
   IST. Time-keeping support for shipping activities in Bombay Harbour was
   provided by the Colaba Observatory in Bombay, which was established in
   1826.

   Most of the towns in India retained their own local time until a few
   years after the introduction of the railways in the 1850s, when the
   need for a unified time–zone became apparent. As headquarters of the
   two largest Presidencies of British India, local time in Mumbai (then
   Bombay) and Kolkata (then Calcutta) assumed special importance, that
   was gradually adopted by the nearby provinces and princely states. In
   the 19th century, clocks at various locations were kept in
   synchronisation through telegraphic means – for example the railways
   synchronised their clocks thorough a time signal which was sent from
   the head office or the regional headquarters at a specified time every
   day.

   In 1884, the International Meridian Conference in Washington, D.C., set
   up uniform time zones across the world. It was decided that India would
   have two time zones, with Kolkata using the 90th east meridian and
   Bombay the 75th east meridian. Calcutta time was set at 5 hours, 30
   minutes, and 21 seconds in advance of GMT, while Bombay time was 4
   hours, 51 minutes ahead of GMT. By the late 1880s, many railway
   companies began to use the Madras time (known as " Railway time") as an
   intermediate time between the two zones. Another time zone, Port Blair
   mean time, was established at Port Blair, the capital of the Andaman
   and Nicobar Islands in the Bay of Bengal. The Port Blair mean time was
   set to 49 minutes and 51 seconds ahead of Madras time.

   British India did not officially adopt the standard time zones until
   1905, when the meridian passing east of Allahabad at 82.5 degrees east
   longitude was picked as the central meridian for India, corresponding
   to a single time zone for the country. This came into force on January
   1, 1906, and also applied to Sri Lanka (then Ceylon). However Calcutta
   time was officially maintained as a separate time zone until 1948.
   IST in relation with the bordering nations.
   Enlarge
   IST in relation with the bordering nations.

   In 1925, time synchronisation began to be relayed through omnibus
   telephone systems and control circuits to organisations that needed to
   know the precise time. This continued until the 1940s, when time
   signals began to be broadcast using the radio by the government.

   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 for a few more years. The Central
   observatory was moved from Chennai to a location near Mirzapur 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.

Problems

   A single, large time zone has been shown to cost more, and requires
   rescheduling of events to make them compatible with the rest of the
   zone or with the day's cycle. 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 Kutch in the far west.
   Inhabitants of the north–eastern states have long demanded a separate
   time zone 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
   Department 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 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."

   Though the government has consistently refused to split the country
   into multiple time zones, provisions in various Indian 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.

Time signals

   In India, 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 Universal Coordinated Time.

   Features of the Time and Frequency Standards Laboratory include :
     * Four caesium and rubidium atomic clocks;
     * 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 \pm 10^{-10} ; and
     * Time and frequency calibrations are made with the help of pico– and
       nanoseconds time interval frequency counters and phase recorders.

   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.

   Retrieved from " http://en.wikipedia.org/wiki/Indian_Standard_Time"
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