Indian Standard Time
The sun rises about two hours earlier in Arunachal Pradesh than in Gujarat, because there is a longitudinal difference of nearly 29 degrees. Yet the whole country keeps one time.
- IST is 5 hours 30 minutes ahead of GMT/UTC.
- It is based on the Standard Meridian of India, 82°30'E, which passes near Mirzapur in Uttar Pradesh. It runs through five states: Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Odisha and Andhra Pradesh.
- Every 1 degree of longitude equals 4 minutes of time, so 15 degrees equals 1 hour.
- The Standard Time of the Meridian is the local time of Mirzapur-Naini area.
- Before 1947, Madras, Bombay and Calcutta had different local times. Indian Standard Time was adopted for the whole country on 1 September 1947.
The one-time-zone debate
| Side | Argument |
|---|---|
| For two time zones | The Northeast loses working daylight; a second zone (about 6 hours ahead of UTC) would save energy and raise productivity. |
| For one zone | Simplicity for railways, aviation and broadcasting; national unity; risk of confusion at the boundary. |
Tea-garden time (Chah Bagan time) in Assam and some NE areas is one hour ahead of IST, an informal local time used since colonial days.
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from NCERT, standard geography textbooks, the Census of India 2011, the India State of Forest Report, IMD, Ministry of Agriculture and other official sources. Maps are schematic teaching maps, not Survey of India maps, and zone boundaries are approximate. Figures such as production, capacity, counts of parks and ports, and census status change, so check the latest official source before relying on them. Found a mistake? Tell us.