Live (computed) · Computed from the Earth's orbit and tilt
Day, night and the seasons
The shaded half of the globe is in night. The Earth's axis is tilted, so through the year the Sun climbs higher and the days grow longer in one hemisphere while they shorten in the other. That, not the distance from the Sun, makes the seasons.
The tilt
The Earth's axis is tilted 23.4° compared with its path around the Sun, and it keeps pointing the same way in space all year. In June the northern hemisphere leans towards the Sun; in December the southern hemisphere does.
Higher Sun, longer days
When your hemisphere leans towards the Sun, the noon Sun climbs higher, so each square metre of ground receives more energy, and the days are longer, so the Sun shines for more hours. Both make summer warm. In winter the low Sun's light is spread over more ground and the nights are long.
Solstices and equinoxes
Around 21 June and 21 December are the solstices, when the noon Sun is overhead on the Tropic of Cancer (23.4° N) or the Tropic of Capricorn (23.4° S). Around 20 March and 23 September are the equinoxes, when the Sun is overhead at the equator and day and night are nearly equal everywhere.
Midnight Sun and polar night
North of the Arctic Circle (66.6° N) the Sun stays up all day around the June solstice and stays below the horizon around the December solstice. Near the poles each lasts for months; the same happens the other way round in the Antarctic.
Distance is not the reason
The Earth's orbit is slightly oval. The Earth is closest to the Sun, about 147 million km, in early January and furthest, about 152 million km, in early July. Northern summer happens when the Earth is furthest away.
The Tropic crosses Taiwan
The Tropic of Cancer crosses Taiwan in Chiayi and Hualien, where monuments mark it. On the June solstice the noon Sun stands almost directly overhead there; in Taipei it reaches 88°, and in December only about 42°.
Did you know?
The Tropic of Cancer creeps south by about 14 m a year at present, because the tilt of the Earth's axis is very slowly decreasing.