The stops
- At noon at Greenwich, in London, the Sun is straight over the Prime Meridian. It moves west 15° every hour, all the way round in 24 hours. So every 15° of longitude is one hour of clock time. The labels along the bottom show the time the Sun gives each place.
- Cairo is 31° east of London, about two hours further along the Sun's path. So when it is noon at Greenwich, the Sun's clock in Cairo reads about 2 in the afternoon.
- Tokyo is 140° east, nine hours ahead. At noon at Greenwich it is already 9 in the evening there, and Japan is on the night side of the Earth.
- New York is 74° west, five hours behind. At noon at Greenwich it is about 7 in the morning in New York, and the Sun has only just come up.
- Real time zones follow borders, not lines. China is as wide as five zones but uses one clock for the whole country. In the far west of China the Sun is overhead at about 3 in the afternoon by the clock. And many countries move their clocks an hour forward in summer, so the clock and the Sun drift apart a little more.
- Halfway round the world, at 180°, is where the date changes. Cross it going west and it is tomorrow; going east, it is yesterday. The International Date Line bends around islands so no country is split in two.
Next
Is the Sun ever straight overhead? Why it never is in London, and why that isn't why the sky is grey.