BharatNotes What is Standard Time and Time Zones?
Local time at any place is determined by the position of the Sun, so every meridian has a slightly different local (solar) time — places to the east see sunrise earlier. Since the Earth completes a 360° rotation in about 24 hours, it turns 15° of longitude every hour, i.e. 1° corresponds to 4 minutes of time. To replace the confusion of countless local times, nations adopt a standard time: a single clock time for the whole country (or region), fixed as a uniform offset from a global reference and calculated from a chosen central/standard meridian.
A time zone is the belt of longitude that keeps this common standard time. In theory the globe is divided into 24 time zones, each 15° wide, centred on the Greenwich Prime Meridian (0°). In practice, because boundaries follow political and administrative lines and some regions use 30- or 45-minute offsets, the number of distinct time offsets in use today is considerably higher than 24.
Key Reference Points
| Concept | Detail |
|---|---|
| Prime Meridian | 0° longitude through Greenwich, London — adopted at the International Meridian Conference, 1884 |
| Global reference standard | UTC (Coordinated Universal Time), atomic-clock based, introduced 1 January 1972; succeeded GMT for precision |
| International Date Line | Roughly along the 180° meridian, opposite Greenwich, in the Pacific |
| Width of one time zone | ~15° of longitude = 1 hour |
Indian Standard Time (IST)
India adopted a single standard time based on the meridian 82°30′E (82.5°E), which passes through Mirzapur (near Prayagraj), Uttar Pradesh. Since 82.5° ÷ 15 = 5.5 hours, and the meridian lies east of Greenwich, IST = UTC+5:30. The Mirzapur meridian was selected as India's central meridian under British administration, with standard time coming into force on 1 January 1906. India does not observe daylight saving time.
The IST meridian (82°30′E) is one of the meridians that passes through India, and notably IST is 5 hours 30 minutes ahead of UTC — one of the few half-hour-offset standard times in the world.
The Two-Time-Zone Debate
India spans nearly 29° of longitude (roughly 68°E to 97°E), so the Sun rises well over an hour earlier in the northeast than in the west. The far east effectively "loses" daylight because clocks run on IST. In 2018, the CSIR-National Physical Laboratory (CSIR-NPL) published a proposal for two time zones — IST-I (UTC+5:30) and IST-II (UTC+6:30) — with a demarcation line near the West Bengal–Assam border, arguing it could improve productivity and save energy in the eastern region. (Assam's tea estates already informally follow "chai bagan"/tea-garden time, an hour ahead of IST.) As of the latest position, the Government of India has not adopted separate time zones, citing concerns over administrative complexity and risks at the date/zone boundary.
UPSC Angle
This is a foundational concept — no single direct PYQ defines it, but it underpins recurring Prelims questions on longitude–time relationships, the Prime Meridian, the International Date Line and IST calculation. Master the arithmetic (15° = 1 hour) and the IST rationale, and link the two-time-zone debate to GS2/GS3 themes of governance, regional productivity and energy efficiency.
