Indian Standard Time: why 82°30′ east is used as the standard meridian
A geography and science note on India’s standard meridian, UTC+5:30 and the value of one national time.
Indian Standard Time is UTC+5 hours 30 minutes and is based on the 82°30′ east standard meridian. A common national time helps coordinate administration, transport and broadcasting across India’s east–west span.
Longitude and solar time
Earth rotates from west to east, so places at different longitudes experience local solar noon at different times. India uses one standard time for civil and administrative coordination. The reference meridian is 82°30′ east, and IST is five hours and thirty minutes ahead of Coordinated Universal Time.
Why a common time helps
One national clock simplifies railway timetables, broadcasting and public administration. It does not mean sunrise or sunset occurs at the same local solar time in every state. For exam questions, distinguish the reference longitude from the UTC offset: the meridian is the geographic reference, while UTC+5:30 is the civil-time offset.
Editorial note
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Frequently asked questions
What is IST’s UTC offset?
UTC+05:30.
Does one national time mean sunrise happens at the same clock time everywhere?
No. Daylight timing still differs across India’s east–west span.