Indian Standard Time (IST): On September 1, 1947, the phenomenon of Indian Standard Time (IST) was introduced to the country as its official time.
- IST is observed throughout the country, with a time offset of UTC + 5.30.
- As per IST, India is five and a half hours ahead of Greenwich Mean Time (GST).
- India does not follow Daylight Saving Time, like other countries in the world.
- Indian Standard Time is adopted from the 82.5 degrees East longitude, the approximate location of a clock tower in Mirzapur near Allahabad and closest to the corresponding longitude reference line.
- All the states and Union Territories across India, currently, share the same time, the Indian Standard Time. But, this is not the case pre-independence.
- Before independence, Kolkata and Mumbai retained their own local time (known as Calcutta Time and Bombay Time) until 1948 and 1955, respectively.
- Due to this, there was a huge confusion among the passengers who travel across the time zones.
- To avoid such confusion, the Indian Government took up a decision to bring the whole country under one Time zone, the Indian Standard Time Zone(GMT+5:30).
- This time is the average of Bombay Time and Calcutta Time.
- The Madras Observatory was established by the British East India Company in 1792 primarily because of the efforts of Michael Topping, a sailor and astronomer.
- In 1802, the first official astronomer of the British East India Company, John Goldingham established the longitude of Chennai as 13°5′24″N, 80°18′30″E, which was five hours and thirty minutes ahead of Greenwich Mean Time.
- It was after this advancement that, for the first time, India’s day began at 12 midnight, instead of sunrise – which was an initial practice.
- Despite Goldingham’s advancement, most towns and cities continued to rely on their own local time measurement systems until the railway system was established in the 1850s.
- In 1884, Mumbai and Kolkata became major centers for the British in India and as they gained prominence, they were established as time zones.
- Kolkata was set at 5 hours and 30 minutes ahead of GMT, and Mumbai at 4 hours and 51 minutes ahead.
- The Central observatory was moved from Chennai to a location at Shankargarh Fort in Prayagraj district so that it would be as close to UTC+05:30 as possible.
- In 1905, the meridian passing east of Allahabad was declared as a standard time zone for the country and was declared as IST in 1947.
Daylight Saving Time (DST) was used briefly during the China–India War of 1962 and the Indo-Pakistani Wars of 1965 and 1971.
IST in Ancient Times in India:
About Surya Siddhanta:
- Surya Siddhanta is a Sanskrit treatise in Indian astronomy in fourteen chapters.
- Earlier in the 4th century CE, an astronomical treatise “Surya Siddhanta” had mentioned Standard Time in India.
- Assuming to which, the earth is spherical.
- The book outlined that the Prime Meridian passed through Avanti (ancient name for the city of Ujjain) at 23°11′N 75°45′E and Rohitaka (ancient name for Rohtak) at 28°54′N 76°38′E.
- The book also elaborates that Rohatika and Avanti are situated on a line that passes through the Equator (76° E) and the North Pole.
- A sidereal day in ancient India began with sunrise at the Prime Meridian in Ujjain and then was divided into smaller time units.
- Despite these early advancements standard time they were mostly used for astrological calculations, and not actual timekeeping.
- Instead, the local kings used the Hindu calendar to keep time in their territories.
- The Jantar Mantar, completed in 1733 in Jaipur, Rajasthan, is evidence of this with its 90-foot-tall sundials used to accurately calculate local time.