The Earth’s movements and the seasons

The Earth rotates on its axis once in 24 hours from west to east; this period is one day. The Sun lights only half of the Earth at a time, so day and night alternate. The Earth goes round the Sun in 365 days and about 6 hours; a year is counted as 365 days, and every four years the extra 6 hours add up to one day, so every fourth year is a leap year and February has 29 days. Because the Earth’s axis is tilted (about 23.5°) relative to its orbit, the Sun climbs to different heights in different seasons and the seasons change. Around 20–21 June (the textbook gives 22 June) the Northern Hemisphere has its longest daylight – the summer solstice; around 21–22 December the shortest – the winter solstice; around 20–21 March (the textbook gives 21 March) and 22–23 September day and night are nearly equal – the spring and autumn equinoxes. The Sun is directly overhead at 23.5° N and 23.5° S – the Northern and Southern Tropics; the lines at 66.5° are the polar circles. These lines divide the Earth into one hot, two temperate and two cold zones; Uzbekistan lies in the temperate zone.