A walk through Indian time from Ujjain to Mirzapur via Greenwich - Hindustan Times

A walk through Indian time from Ujjain to Mirzapur via Greenwich

Dec 27, 2023 08:37 PM IST

As things stand now, the vast breadth of India follows a single time zone based on the Mirzapur line, midway between the country’s eastern and western extremes

Some 16 to 17 centuries ago, the line of longitude passing through Ujjain, located 72°46’ east of Greenwich, was considered the line of zero longitude by Indian astronomers.

Sun Dial "Jantar Mantar at the Ved Shala (Observatory), Ujjain(Gyanendra Singh Chauhan/WikiCommons) PREMIUM
Sun Dial "Jantar Mantar at the Ved Shala (Observatory), Ujjain(Gyanendra Singh Chauhan/WikiCommons)

This was the meridian that Madhya Pradesh chief minister Mohan Yadav was referring to when he asserted that Ujjain is the “global prime meridian” and promised to “correct the time of the world”.

To be sure, the Ujjain meridian was not “global” in the sense that it was never used globally. From the viewpoint of the ancient Indians who used it, however, it was indeed global, for they believed that the line divided the inhabited world in half.

The meridian, which is referenced in the Sanskrit text Surya Siddhanta (fourth to fifth centuries CE), passed through Lanka, where it was assumed to cross the equator (the equator actually lies south of Sri Lanka), while Ujjain was placed on the Tropic of Cancer (this was accurate).

Ujjain was thought to be the centre of the inhabited world. The day, therefore, began when the sun rose in the city. At 90° west and east of the meridian, the ancients placed the cities of Romaka (Yavanapura) and Yamakoti. The inhabitable world existed north of the equator between Yavanapura and Yamakoti. (Gerald Tibbets, History of Cartography).

Today, Indian Standard Time (IST) is based on the line of longitude through Mirzapur, a little under 10° east of Ujjain. The Mirzapur meridian is 82°30’ east of the Greenwich Prime Meridian, now the global standard reference.

Other meridians

All this does not mean that Ujjain and Mirzapur were the only meridians India has ever used, nor that Greenwich was the only meridian used elsewhere. Ever since humans introduced the concept of longitudes, there have been countless meridians around the world, each locally considered longitude zero.

The idea of longitudes itself made this inevitable. These lines divide the Earth, then assumed to be spherical, into 360 degrees. Since the Earth takes 24 hours to spin these 360 degrees, every hour is represented by 15 degrees, and every degree represents 4 minutes. All these calculations were based on observations of the Sun, and where else would one place the line of zero longitude but at an observable place?

Greek astronomers of the second century BCE assumed that the line of zero longitude passed through Alexandria in Egypt. Four centuries later, the Alexandrian polymath Ptolemy used a prime meridian that passed through the Canary Islands.

The work of the ancient Indian astronomers, meanwhile, went on to influence the Arabs. The polymath al-Khwarazmi (780-850 AD) based his astronomical handbook, the zij, on the meridian through Ujjain, which came to be known as Arin in Arabic texts. (Raymond Mercier, History of Cartography)

India adopted the Greenwich-based meridian through Mirzapur after Independence. But it was not a direct transition. In between, the British introduced Madras Time in 1802 (8:16 minutes behind what is IST today), followed by Bombay Time (39 minutes behind IST) and Calcutta Time (23:20 minutes ahead of IST). The latter two came in 1884, shortly after GMT was universally adopted that year.

Greenwich goes global

The Royal Observatory at Greenwich, UK, founded in 1675, calculates the mean time when the sun crosses the observatory. Mean time is clock time, as opposed to solar time which varies from day to day because the sun crosses the meridian at different times on different days through the year. A day according to GMT runs from one midnight to the next, as opposed to the ancient practice that took sunrise as the beginning of the day.

In 1767, the work of astronomer Nevil Maskelyne brought GMT to a wider audience. He introduced the Nautical Almanac with tables that enabled sailors to determine their Greenwich-based longitude, and therefore their position at sea. Greenwich-based longitudes thus became a standard for sailors.

On land, as the railway network expanded, GMT officially became railway time in 1847, and Britain’s legal standard time in 1880.

In 1884, the Greenwich meridian became the prime meridian of the world, a decision taken at the International Meridian Conference in Washington DC. According to the Royal Observatory website, there were two main reasons for this. One, the US was already calculating its own time zones using Greenwich as the reference. Two, at that time, 72% of the world's commerce depended on sea charts that used Greenwich as the prime meridian.

India’s transition

In the very early days of British India, especially after the introduction of railways, local time was observed in each large city. Bombay and Poona (now, Mumbai and Pune) for instance, had their own local times differing by about seven minutes, while Ahmedabad strangely observed Madras time, former South Western Railway AGM PK Mishra wrote on the Indian Railways website.

When Bombay Time and Calcutta Time were introduced in 1884, they were followed for many official purposes but the railways continued to use Madras Time. This time zone was eventually phased out in 1906, when the British adopted Indian Standard Time based on a meridian through Allahabad, roughly 5:30 hours ahead of Greenwich.

It was only in 1947, that independent India adopted IST as we know it today, based on the meridian through Mirzapur, less than a degree east of Allahabad.

As things stand now, the vast breadth of India follows a single time zone based on the Mirzapur line, which is midway between the country’s eastern and western extremes. It goes without saying that Mirzapur’s longitude of 82°30’ is based on the prime meridian at Greenwich, not Ujjain.

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    Puzzles Editor Kabir Firaque is the author of the weekly column Problematics. A journalist for three decades, he also writes about science and mathematics.

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