The stops
- The Earth leans over by 23.4°. As it travels round the Sun over a year, the lean keeps pointing the same way, so first the north and then the south tips towards the Sun. The little sun marks where the Sun is straight overhead today.
- 21 June. The north leans towards the Sun, which is straight overhead on the Tropic of Cancer. Days in the north are long, and it is summer there. Inside the Arctic Circle, the Sun does not set at all.
- 21 December. Now the south leans towards the Sun, which is overhead on the Tropic of Capricorn. It is summer in Australia and South Africa, and inside the Arctic Circle it stays dark all day.
- Around 20 March and 22 September, neither half leans towards the Sun. It is overhead on the Equator, and day and night are about 12 hours long everywhere. These two days are the equinoxes.
- Autumn in the north. Each day the Sun climbs a little less high and sets a little earlier. With less light, trees stop making the green chlorophyll in their leaves, so the yellow and brown underneath show through. Then the leaves dry out and fall, and the tree rests until spring.
- Near the Equator the Sun is high all year, so there is no cold winter. The seasons are wet and dry instead. In West Africa, from about November the Harmattan wind blows dust in from the Sahara, the air dries out, and many trees drop their leaves too.
- So the seasons are opposite in the two hemispheres. When it is autumn in London, it is spring in Sydney, and Christmas there falls in summer.
Next
What time is it there? Why it is morning in New York while it is evening in Tokyo.