Time Zones in India

Clock time and solar time in India

A country's clocks are a political choice, not an astronomical one, so they rarely line up with its own sun. Measured against local solar time, the clock in Mumbai runs 38 minutes ahead of the sun, while in Kolkata it runs 23 minutes behind the sun.

That is a spread of 1 hour 2 minutes between the two ends of India's tracked cities, all of it the result of longitude rather than of the clock. The wider that gap, the more one shared office schedule means genuinely different amounts of morning light depending on where you are.

How much daylight changes through the year

Daylight is governed by latitude, not by the clock. Delhi, at 28.6° north, gets 13 hours 58 minutes of daylight on the longest day of the year and 10 hours 19 minutes on the shortest.

Bengaluru, at 13.0° north, gets 12 hours 53 minutes of daylight on the longest day of the year and 11 hours 22 minutes on the shortest. So the annual swing between longest and shortest day is 3 hours 39 minutes in Delhi against 1 hour 32 minutes in Bengaluru, within the same country.

Related reading

• The world's strangest time zone offsets, and why half-hour and 45-minute zones exist
• Why a very wide country might still run a single clock
• The countries that gave up on daylight saving, and why agreeing what to keep is the hard part