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Indian Time Zone

India is a vast country having longitudinal extent between 68°7'E to 97°25'E. So, the whole country could be divided into several time zones which would be a problem from standardization point of view. Therefore, Indian Standard Time was devised to keep away the anomaly. Today we observe +5.30 hours ahead of Greenwich Mean Time as Indian Standard Time (IST). Indian Standard Time is also observed in Sri Lanka.

The longituted of India which is taken for the purpose of calculating Indian Standard Time is 82.5° E longitude. The place located on this longitude is Mirzapur, a city situated near Allahabad in the Indian State of Uttar Pradesh. The geographical coordinates for Mirzapur is 25.15°N 82.58°E which coincides with the location of the city and therefore is taken as a reference point for calculating Indian Standard Time.

The differences of Indian Standard Time (IST) and other places located in different countries vary from one place to other depending upon the longitudes of the place. For example, IST is (+)12.5 hours, (+)9.5 hours and (+)5.5 hours ahead of the west coast of the USA (Los Angeles, San Fransisco, San Diego), the east coast of the USA (New York, Florida), of the UK respectively and (-)4.5 hours behind Australia (Melbourne, Sydney, Brisbane). This could well be understood by an example. If India clocks the time 12 p.m. noon on 1st February, then the time clocked in west coast of USA is 11.30 p.m. (midnight) of 31st January, 2.30 a.m. (early morning) of 1st February in the east coast of USA, 6.30 a.m. (morning) of 1st February in UK and 4.30 p.m. (evening) of 1st February in Australia.

It is noteworthy that India does not adjust Daylight Saving Time (DST) or seasonal variations in its standard time. Daylight Saving Time (DST) was the term devised for a short period during the war period between India and China in 1962 and with Pakistan in 1965 and 1971. The adjustment was important for adjusting the time differential of different places falling on different geographical coordinates. For the purpose of military and aviation use Indian Standard Time is termed as - E*, an abbreviation of “Echo-Star".


Before independence, different timing were observed at different places. There was Bombay Local Time( now Mumbai) and Calcutta Local Time (now Kolkata). On the other hand, the observatory of the Central government was located at Madras (now Chennai). After gaining independence, India established its official time and came to be known as Indian Standard Time (IST) in 1947. But the local timings were continually observed by Bombay and Calcutta till 1955. Finally, to ward away with the anomalies, Indian Government shifted its Central observatory from Madras (Chennai) to a location near Mirzapur, the geographical coordinates of which coincided with +5:30 GMT.

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