What time is it there?
It is noon in Kathmandu. What time is it in London, Delhi, Tokyo or New York? Pick two cities and see how the turning Earth gives every country its own clock time, and why Nepal is 5 hours 45 minutes ahead of London.
Core concept
The Earth turns 360° in 24 hours, so 15° of longitude is 1 hour: places to the east see the sun first and their clocks are ahead; each country sets its standard time from a longitude near its middle
Topic: Our planet and sky
The Earth turns once a day from west to east, 360° in 24 hours, which is 15° every hour. So when it is noon in one place, the sun has already passed overhead in places to the east, and has not yet reached places to the west. Each country picks a standard time for its clocks, counted from the time at Greenwich in London (0° longitude), called UTC. Nepal's standard time is set at 86.25° E, so Nepal is 86.25 ÷ 15 = 5.75 hours, or 5 hours 45 minutes, ahead of UTC. India is 5 hours 30 minutes ahead, Bangladesh 6 hours, Japan 9 hours, and New York, far to the west, 5 hours behind.
What you will learn
- Explain why 15° of longitude makes 1 hour of time.
- Find the time difference between two cities from their offsets.
- Work out the clock time in another city, including going past midnight.
Before you start
- Know what longitude is.
- Know that 1 hour = 60 minutes.
Materials
- A globe or a world map with longitudes
Equipment
- None
Procedure
- Record noon in Kathmandu against London.
- Change the other city to Delhi, then Tokyo, and record each.
- Change it to New York and record: is it still the same day there?
How this simulation is simplified
- Offsets from UTC: Kathmandu +5:45, Delhi +5:30, Dhaka +6:00, London 0, Tokyo +9:00, New York −5:00 (standard time, no summer clock change).
- It is 12:00 noon in the home city; the time there is shown on a 24-hour clock.