Indian Standard Time

1. Time Zones

The worldwide system of time zones was proposed by a Scottish-Canadian engineer – Sir Sandford Fleming, in 1879. Eventually, in 1884, the International Meridian Conference adopted a 24-hour day. Countries across the world keep different times due to Earth’s rotation and revolution around the Sun.

2. World Time Zones

We have 24 different time zones in the world. Because the Earth rotates 360° every 24 hours, each time zone is 15° longitude apart from the other.


The Prime Meridian (Greenwich Meridian) defines the center of the first time zone in the world. This means the Prime Meridian time zone spans from 7.5°W to 7.5°E. Then, the next time to the east spans 7.5°E to 22.5°E.

2.1. Gaining and losing time

When you move to the right, you gain time (fast time). In other words, for every time zone that you move toward the right, you add one hour. But when you head toward the left, you lose an hour (slow time).

You can find any time by counting how many degrees of longitude it is away from Greenwich. For example, it would be 4 pm at 60°E longitude when it’s noon at the Prime Meridian. Whereas it would be 8 am at 60°W longitude

2.2. International Date Line

The International Date Line is a north-south line in the Pacific Ocean where you turn your calendar back or ahead one day. The center of the time zone roughly follows 180° longitude without crossing any landmass.

When you cross the International Date Line moving toward the east, you turn your calendar back one day. Whereas when you go from the west across the International Date Line, you turn your calendar ahead one day.

2.3. Irregular Time Zone Boundaries

No time zone in the world runs a perfect north-south line. Instead, they are jagged and adapt to the political boundaries of countries. Also, there can be “irregular square” time zones similar to islands.

For example, the province of Newfoundland and Labrador contains its own time zone with the same name that is UTC -3:30. But the province mostly observes Atlantic Standard Time (AST). Other examples include Afghanistan, Venezuela, and Australia with unusual time zones.

3. Time Standard v/s Time Zone:

A time standard is a means of measuring time. This can be done either naturally, by our changing view of the sun as the earth rotates daily on its axis, or by artificial means such as using atomic clocks.

A time zone is the agreed time standard used within a specific geographical area. It’s essentially based on local time and longitude but may be modified by an hour or two as per convenience.

4. Indian Standard Time

Indian Standard Time(IST) represents the time observed throughout India, with a time offset of UTC+5:30. India opted out of observing daylight saving time, (DST) or other seasonal adjustments, although briefly using DST during the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971.

Indian Standard Time calculates on the basis of 82.5° E longitude, 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 30 minutes. A clock tower at the Allahabad Observatory (15° N 82.5° E) calculates local time, though the National Physical Laboratory, in New Delhi has been entrusted with the official time-keeping devices.

4.1. History of IST

Most 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. Local time in Mumbai(then Bombay) and Kolkata (then Calcutta), as headquarters of the two largest Presidencies of British India, assumed special importance, the nearby provinces and princely states gradually adopted the standard. In the 19th century, telegraph kept the clocks in synchronization– for example the railways synchronized their clocks thorough a time signal 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, India receiving two time zones, with Calcutta using the 90th east meridian and Bombay the 75° E meridian. The Conference set Calcutta time at 5 hours 30 minutes 21 seconds ahead of GMT, while setting Bombay time at 4 hours 51 minutes ahead.

By the late 1880s, many railway companies began to use Madras time (known as “Railway time”) as an intermediate time between the two zones. The British colonial government established another time zone, Port Blair mean time, established at Port Blair, the capital of the Andaman and Nicobar Islands in the Bay of Bengal. They set Port Blair mean time to 49 minutes 51 seconds ahead of Madras time.

British India officially adopted the standard time zones in 1905, when picking the meridian passing east of Allahabad at 82.5° E longitude as the central meridian for India, corresponding to a single time zone for the country. That came into force on January 1, 1906, also applying to Sri Lanka (then Ceylon). Calcutta time remained as an official, separate time zone until 1948.

In 1925, the government began relaying time synchronization through omnibus telephone systems and control circuits to organizations that needed to know the precise time. That continued until the 1940s, when the government began to broadcast time signals using the radio. 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 moved from Chennai to a location near Mirzapur, as close as possible to UTC +5:30. During the Sino–Indian War of 1962 and the Indo–Pakistani Wars of 1965 and 1971, the government resorted briefly to daylight saving time as a way of reducing civilian energy consumption.

4.2. Issues with IST

The country’s east–west distance of more than 2,000 km (1,200 miles) covers over 28 degrees of longitude, resulting in the sun rising and setting almost two hours earlier in the north-eastern Seven Sister States than in the Rann of Kutch in the far west. 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 government rejected the recommendations 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, presented to Parliament in 2004 by the Minister for Science and Technology, Kapil Sibal, recommended maintaining the current 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 labor laws such as the Plantations Labour Act, 1951allow the Central and State governments to define and set the local time for a particular industrial area.

An August 2007 article in the Current Science journal estimated that the evening peak energy demand could be reduced by as much as 16 percent by setting Indian Standard Time six hours ahead of Universal Coordinated Time instead of the present 5.5 hours. According to the authors, the money value of the savings accrued as a result of the time change would be in the range of Rs 1,000 crore every year.

4.3. Two-Time Zones for India

4.3.1. Need for Two-Time Zones

  • Large Geographical Extent:

India is geographically the second-largest country (after China) to not have multiple time-zones. India stretches from 97°25’E in Arunachal to 68°7’E in Gujarat — almost 30 degrees of longitude which is more than enough to have two time zones.

  • Early Sunrise and Sunset:

The demand for two time zones rose because northeastern India (NER) and the Andaman and Nicobar islands (ANI), due to their geography, witness an early sunrise and sunset relative to the rest of the country. The NER has long complained about the effect of a single time zone on their lives and their economies, they lose important daylight which can be used productively as the sun rises as early as 4 am in summer while the government offices open at 10 am.

  • Sync with Circadian Rhythm:

Many people in India operate in a time zone that is not an appropriate diurnal cycle for them, people’s productivity and efficiency follows a biological clock that is synchronized with the daily light-dark cycles. From the body’s circadian rhythm point of view, the existing IST is highly suitable for Kanyakumari, Kavaratti, and Ghuar Mota, manageable for Alipurduar, Kolkata, Gangtok, Mirzapur and Gilgitum, but highly unsuitable for Dong and Port Blair.

Circadian Rhythm

Circadian rhythm is the 24-hour cycle that tells our bodies when to sleep, rise, and eat—regulating many physiological processes. Internal body clock is affected by environmental cues like sunlight and temperature and determines whether one feels wide awake and energized or tired.

  • CSIR’s Suggestions:

In 2006, the erstwhile Planning Commission recommended the division of the country into two time zones. CSIR- NPL has supported the long-standing demand and has suggested two ISTs separated by a difference of one hour:

  • IST-I for most of India (covering the regions falling between longitudes 68°7′E and 89°52′E).
  • IST-II for the Northeastern region (covering the regions between 89°52′E and 97°25′E).

4.3.2. Benefits of having two Time Zones in India

  • The research paper by National Physical Laboratory establishes that India’s potential savings in energy consumption could be around 20 million kWh a year if it follows two time zones as it helps in the usage of many daylight hours, which are now being wasted in the eastern region.
  • Synchronises sunrise and sunset timings with office hours. People will be able to work better and plan better, according to natural cycles.
  • We would have healthier and happier people who adhere to their circadian rhythm. Even now, unofficially, the tea gardens of Assam have been following ‘Chaibagaan time’ which is one hour ahead of the IST.
  • A reduction in energy consumption will cut down India’s carbon footprint. Thus boosting India’s resolve to fight climate change.

4.3.3. Problems of having two time zones:

  • The possibility of rail accidents would increase because of the two Time zones. Railway signals are not fully automated, and many routes have single tracks.
  • Resetting clocks with each crossing of the time zone.
  • The overlap between office timings reduces if there are two time zones. Important sectors like banks, industries and MNCs would face difficulties in adjusting to the new time zones.
  • The marking of the dividing line of the two zones would be a problem.
  • Two time zones can have adverse political consequences as India apart from getting divided on the lines of religion, caste, race, language, etc, now will get divided on the lines of Time Zones.

4.4. Alternatives to Two-Time-Zoning

4.4.1. Time Shifting IST

The National Institute for Advanced Science (NIAS) cited that a Permanent shift of IST to 30 minutes will be better than two time zones i.e., 6:00+ UTC to 90°East. In a four-decade-old study concluded by NIAS, it suggested that advancing the IST by 30 minutes would help India boost productivity, save energy and bring the North East into the mainstream fold. Doing so would translate into a heft saving of energy of 2.7 billion units (as of 2009 estimates, which works out to nearly 3.5 billion units as of today).

There are also other Asian countries that have implemented a one-time advancement in their clocks – China, Kyrgyzstan, Malaysia, Singapore, and South Korea.

4.4.2. Daylight Saving Time

DST is a seasonal time change measure where clocks are set ahead of standard time during part of the year. As DST starts, the Sun rises and sets later, on the clock, than the day before. Today, about 40% of countries worldwide have DST to make better use of daylight and conserve energy. How Does Daylight Saving Time Work?

When Daylight Saving Time (DST) begins, we lose an hour. When it ends, we gain an hour. Spring Forward in Spring

When DST starts in the spring, our clocks are set forward by a certain amount of time, usually by one hour. This means that one hour is skipped, and on the clock, the day of the DST transition has only 23 hours.

Since DST switches usually occur at night to avoid disrupting public life, they snatch away an hour of our usual sleeping time, forcing us to adjust our body clocks. If you set your alarm to the same time as before the clock change, you will sleep an hour less. The good news is that if you work a night shift, you will get away with working one hour less that night. Example of DST Start

The DST period in the United States begins at 02:00 (2 am) local time, so the hour from 2:00:00 to 2:59:59 does not exist on the night of the switch. It is skipped as clocks spring forward from 1:59:59 standard time to 3:00:00 Daylight Saving Time (see table). Fall Back in Fall

In the fall (autumn), the DST period usually ends, and our clocks are set back to standard time again. In terms of hours on the clock, we gain one hour, so the day of the transition is 25 hours long.

In effect, one hour is repeated as local time jumps from DST back to standard time. Let\’s say that clocks fall back from 2 to 1 o\’clock. This means that the hour between 1 and 2 o\’clock happens twice during the night of the switch.

It also means that a time like 01:30 (1:30 am) refers to two different moments, which are one hour apart. So if you\’re out to meet somebody during that hour—which really lasts two hours—make sure to specify if the meeting is before the switch (first hour) or after it (second hour). Example of DST End

In the United States, DST always ends at 02:00 (2 am) local time, and clocks are set back to 01:00 (1 am). The table below shows the moment when the time first reaches 1:59:59 and clocks jump back to 1:00:00 standard time and begin ticking towards 2 o\’clock for a second time. When the repeated hour is over, local time goes from 1:59:59 to 2:00:00, just like on any other day.

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