What is the International Date Line? The International Date Line (IDL) passes through the Pacific Ocean. It is an imaginary line, like longitudes and latitudes. The time difference on either side of this line is 24 hours. So, the date changes as soon as one crosses this line. Some groups of Islands (Polynesia, Melanesia, Micronesia) fall on either of the datelines. So if the dateline was straight, then two regions of the same Island Country or Island group would fall under different date zones. Thus to avoid any confusion of date, this line is drawn through where the sea lies and not land. Hence, the IDL is drawn in a zig-zag manner. The International Date Line (IDL) passes through the Pacific Ocean. It is an imaginary line, like longitudes and latitudes. The time difference on either side of this line is 24 hours. So, the date changes as soon as one crosses this line. Some groups of Islands (Polynesia, Melanesia, Micronesia) fall on either of the datelines. So if the dateline was straight, then two regions of the same Island Country or Island group would fall under different date zones. Thus to avoid any confusion of date, this line is drawn through where the sea lies and not land. Hence, the IDL is drawn in a zig-zag manner.

Indian Standard Time

Indian Standard time (IST) is the time zone observed throughout India, with a time offset of UTC+05:30. India does not observe daylight saving time or other seasonal adjustments. In military and aviation time IST is designated E* (“Echo-Star”). Indian Standard Time is calculated on the basis of 82.5°E longitude in the city of Mirzapur, Uttar Pradesh, which is situated approximately on the corresponding longitude reference line. The Republic of India uses only one-time zone across the whole nation and all its territories, called Indian Standard Time (IST), which equates to UTC+05:30, i.e. five and a half hours ahead of Coordinated Universal Time (UTC). India presently does not observe daylight saving time (DST or summer time). The official time signal is given by the Time and Frequency Standards Laboratory. The IANA time zone database contains only one zone pertaining to India, namely Asia/Kolkata. The date and time notation in India shows some peculiarities.

History

Ancient India

See also: Hindu units of time and History of measurement systems in IndiaHindu units of time—largely of mythological and ritual importance—displayed on a logarithmic scale. One of the earliest known descriptions of standard time in India appeared in the 4th century CE astronomical treatise Surya Siddhanta. Postulating spherical earth, the book described the thousands of years old customs of the prime meridian, or zero longitudes, as passing through Avanti, the ancient name for the historic city of Ujjain, and Rohitaka, the ancient name for Rohtak (28°54′N 76°38′E), a city near the Kurukshetra. 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.

During British colonial rule

In 1802 Madras Time was set up by John Goldingham and this was later used widely by the railways in India.^[8] Local time zones were also set up in the important cities of Bombay and Calcutta and as Madras time was intermediate to these, it was one of the early contenders for an Indian standard time zone.^[9][10] Though 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 (UTC+05:30). Indian Standard Time 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 and Bombay Time until 1955.

Chaibagaan Time

The chaibagaan time or the bagaan time refers to the daylight saving the schedule introduced by the British for the better energy savings on the tea plantation more than 150 years ago. But, according to it Assam will turn its clocks 1 hour ahead.Well, the IST corresponds to the time schedule along 82.5 degrees East longitude, where the Mirzapur in UP is located. States to the east of the longitude have less the daylight hours in comparison to the rest. And, this is because even though rises earlier than the rest of India they go to work at the same time.

Thus the turning clock one hour ahead helps utilize precious daylight. Obvious benefits are savings in electricity costs and increase in productivity. Additional daylight hours in the evenings would also be people-friendly, would help save power at home and in offices, reduce petty crimes among other gains. 150 years ago British colonialists introduced “chaibagaan time” or “bagaan time”, a time schedule observed by tea planters, which was one hour ahead of IST.

This was done to improve productivity by optimizing the usage of daytime. After Independence, Assam, along with the rest of India, has been following IST for the past 66 years. The administration of the Indian state of Assam now wants to change it’s time zone back to Chaibagaan time to conserve energy and improve productivity. Indian government didn’t accept to such a proposal. 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. Briefly during World War II, clocks under Indian Standard Time were advanced by one hour, referred to as War Time. This provision lasted from September 1, 1942 to October 15, 1945.

After independence

After independence in 1947, the Indian government established IST as the official time for the whole country, although Mumbai and Kolkata retained their own local time for a few more years. In 2014 Assamese politicians proposed following a daylight-saving schedule that would be ahead of IST by an hour, but as of March 2020, it has not been approved by the central government.

Former practices

Former timezones

Older time zones, not in use any more since introduction of standardised same time zone across India, were:

• Bombay Time (UTC+04:51)
• Madras Time (UTC+05:21:14)
• Calcutta Time (UTC+05:53:20)
• Port Blair mean time (UTC+06:10:37)

Former daylight saving

India and the Indian subcontinent observed “daylight saving (DST)” during the Second World War, from 1942–1945. 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.

Present time zone

India uses UTC+5:30.

Demand for changes Time

In 2014 Assamese politicians proposed following a daylight-saving schedule that would be ahead of IST by an hour, but as of March 2020 it has not been approved by the central government.

((Updated: January 03, 2014, 10:49 am IST)) Assam Chief Minister Tarun Gogoi is campaigning to scrap India’s single time zone, which causes problems for easterners who face summer sunrise as early as 4:30 am. Despite India’s vast size, it has one time of +5:30 from Greenwich Mean Time for its 1.2-billion population, spread from points further east than Bangladesh to the western Arabian Sea. At this time of year, the sun rises in the east shortly before 6 am, more than 90 minutes earlier than in the west, while daybreak in the east comes as early as 4:30 am around the summer solstice. “We need a local time for Assam and the other northeastern states which will be ahead of the Indian Standard Time (IST) by at least an hour to 90 minutes,” said Mr Gogoi.  “We have an early daybreak in the northeast compared to other parts of India and if we have a separate time zone then it would undoubtedly be very productive for all of us and would also help in saving energy,” he added. He plans to lobby in New Delhi for a change, renewing a campaign which last gathered momentum in 2010. Mr Gogoi says sticking to Indian Standard Time means a loss of daylight hours and an attendant decrease in productivity for his state. For instance, a farmer in Assam can start work one hour before her or his counterpart in a state like Gujarat He points out that tea gardens in Assam have for years set their clocks an hour ahead of the rest of the country. The proposal for a different time zone will have to be cleared by the Centre. (Source:- https://www.ndtv.com/india-news/india-could-get-second-time-zone-with-assam-one-hour-ahead-546592)

In June 2017, Department of Science and Technology (DST) indicated that they are once again studying feasibility of two time zones for India. Proposals for creating an additional Eastern India Time (EIT at UTC+06:00), shifting default IST to UTC+05:00 and Daylight saving (Indian Daylight Time for IST and Eastern India Daylight Time for EIT) starting on 14 April (Ambedkar Jayanti) and ending on 2 October (Gandhi Jayanti) was submitted to DST for consideration.^[