. How is India's standard time derived?
Answers
Indian Standard Time (IST) is the time observed throughout India, with a time offset of UTC+05:30. It is calculated on the basis of 82.5' E longitude, in Mirzapur (Amravati Chauraha), Uttar Pradesh, which is nearly on the corresponding longitude reference line.
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Explanation:
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).
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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.