Indian Standard Time

Location of Mirzapur and the 82.5° E latitude 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 1971. In certain time-zone maps, IST is designated as E*.

Indian Standard Time is calculated on the basis of 82.5 °E longitude which just west of the town of Mirzapur, near Allahabad in the state of Uttar Pradesh. The latitude difference between Mirzapur and the Royal Observatory, Greenwich in the UK 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 / 25.15; 82.5) though the official time servers are located in New Delhi.

History

John Goldingham is credited with the establishment of the current fractional time zone (UTC+5:30).

One of the earliest standards of time measurement in India comes from the Hindu astronomical treatises like the Vedas. According to them, the Prime Meridian (or zero longitude) passed through the historic city of Ujjain (23°11′N 75°45′E). The time of sunrise in the city on the day of Makar Sankranti marked the beginning of calender year. For most of India's history, ruling kingdoms kept their own local time. These kingdoms typically used precise mathematical models of years and days according to the Hindu calendar. Both lunar and solar units were extensively used for keeping time. The smallest unit of measuring time, the vipala (based on solar day), was equivalent of 0.4 seconds. Time observations and measurements were made with vipala as the least count. The Jantar Mantar built by Maharaja Sawai Jai Singh in Jaipur in 1733 contained large sundials which were used to accurately determine the local time.

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, nominated 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, the first-ever instance of the use of the current time zone. 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 the Bombay port 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, gradually being adopted by the nearby provinces and princely states.

In 1884, the International Meridian Conference in Washington, D.C. set up uniform time zones across the world. It was decided that India was to have two time zones, with Kolkata using the 90th east meridian and Bombay the 75th east meridian. Calcutta time was set at five hours, 30 minutes, and 21 seconds in advance of GMT, while Bombay time was four hours, 51 minutes ahead of GMT. However, 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. There, 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.

Bombay time faced more difficulties converting to IST. During that period (1905) in Mumbai, Bal Gangadhar Tilak, a prominent freedom fighter of the Indian independence movement was put on trial in a bomb blast case. Taking advantage of the prevailing anti-government public sentiment over the trial, prominent barrister Pherozeshah Mehta argued against the time change by stalling moves to adopt IST by the Bombay Municipal Corporation. His argument that the government did not take the people into confidence led to the government's shelving of the conversion to avoid the further antagonisation of the public. Bombay time was thus maintained until 1955.

IST in relation with the bordering nations.

After India's 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

With an east-west distance of over 2,000 km (1,200 mi), the sun rises and sets an hour earlier in eastern India than in the west. Inhabitants of India's 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 ternary system included Bhopal in Madhya Pradesh at the centre of an intermediate time zone. The recommendations were not realised.

In 2001, the Indian government established a four-member committee under the Science and Technology Department to examine the need for multiple time zones and daylight saving. The committee did not recommend changes to the unified system.

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 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.

See also

• Hindu astrology

External links

• National Physical Laboratory