Q.While the sun rises earlier in the east, say Nagaland, and also sets earlier, how do the watches at Kohima and New Delhi show the same time?

The watches at Kohima and New Delhi show the same time because both places follow Indian Standard Time (IST), which is a single standard time for the entire country. This standard is based on the longitude that passes through Mirzapur, near Allahabad, and is set at 82.5°E. Even though the sun rises and sets earlier in the east, like in Nagaland, the watches are not adjusted to local solar time. Instead, the whole nation uses one uniform clock time, so a watch in Kohima reads the same hour and minute as one in New Delhi, r …

The sun does rise earlier in Nagaland than in Delhi. That is a fact of geography, not a quirk of clocks. The earth spins from west to east, so the eastern edge of any country catches the first light. Kohima, sitting near the 94th meridian, sees dawn well before New Delhi, which lies around the 77th meridian. If every place simply followed its own local solar time, a Kohima watch would read nearly an hour ahead of a Delhi watch at the same instant. But it doesn't, and the reason is a deliberate human choice: standard time.

Before railways and telegraphs, every town in India — as everywhere — ran on its own local time, judged by the sun overhead. A traveller moving from Calcutta to Bombay would have to reset his watch several times. That was tolerable when journeys took weeks. But when the British built a vast railway network in the nineteenth century, chaos loomed. A single timetable needed a single clock. So the country adopted one standard meridian, 82.5° east of Greenwich, which passes through Mirzapur in Uttar Pradesh, near Allahabad. This line was chosen because it runs roughly through the middle of the country, so the difference between the eastern and western extremes of India stays within a reasonable band — about an hour at most.

The effect is simple. Every watch in India, from Kohima to Kutch, is set to the local time of that 82.5° meridian. When the sun is overhead at Mirzapur, it is twelve noon everywhere in the country, even though in Kohima the sun has already passed its highest point and in Delhi it has not yet reached it. The watch does not follow the sun in your sky; it follows the sun on an imaginary line hundreds of kilometres away. That is why a Kohima clock and a Delhi clock agree, even though their skies disagree.