India stretches from 68°E to 97°E longitude — a span of nearly 30 degrees. Without a single standard time, the sunrise time in Arunachal Pradesh would be about 2 hours earlier than in Gujarat, creating massive confusion. To solve this, India adopted a Standard Meridian.
India is one of the few large countries with a single time zone for the entire nation. By comparison, the USA has 6 time zones and Russia has 11! The biggest time difference between any two places in India is about 2 hours.
India's Standard Meridian is 82.5° East Longitude (82°30'E).
This gives India its official time zone: IST (Indian Standard Time) = UTC + 5 hours 30 minutes
(82.5° ÷ 15° per hour = 5.5 hours ahead of Greenwich/UTC)
The 82.5°E meridian passes through the town of Mirzapur in Uttar Pradesh. The Naini Clock Tower in Mirzapur is maintained as the official IST reference point.
The meridian also passes through:
The longitude 82.5° was chosen because:
India made a political decision to maintain national unity. Having one time zone simplifies railway, airline, and broadcasting schedules across the country. However, Assam and northeastern states find the IST inconvenient as it gets dark very early.
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