Wednesday, September 2, 2009

Indian Standard Time

Indian Standard Time (IST) is the time observed throughout India and Sri Lanka, with a time offset of UTC+05:30. 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 1971. In military and aviation time, IST is designated E* ("Echo-Star").
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.


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 and Rohitaka the ancient name for Rohtak 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 day used by ancient Indian astronomers 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 astronomical day, contains 60 ghalikās. A nakṣatra māsa, or astronomical month, consists of 30 days

Taking a day to be 24 hours, 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 local time to the standard time of Ujjain. Despite these early advances, standard time was not widely used outside 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 (27 m) high, which were used to accurately determine the local time.

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

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.

Time Zones

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[citation needed]. 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 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 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 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.
Recently there had been suggestion to advance the Indian Standard Time by half-an-hour.

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 clocks and are synchronised with the worldwide system of clocks that support the Coordinated Universal 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 ±10−10; and
  • Time and frequency calibrations 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.

Ref :

No comments:

Post a Comment