The solar system, the spinning Earth and the seasons

The seasons are caused by the tilt of the Earth’s axis together with its year-long trip around the Sun (365¼ days). They are not caused by the Earth being nearer to the Sun: in fact the Earth is a little closer to the Sun in early January, when it is winter in Egypt. In summer the north end of the axis leans towards the Sun, so the Sun is higher and the days are longer. In winter it leans away, and in spring and autumn it leans neither way. At the equinoxes in spring and autumn, day and night are about equal. The longest day is at the summer solstice, about 21 June, and the shortest at the winter solstice, about 22 December. In Egypt daylight lasts about 12 hours at the equinoxes, about 14 hours in midsummer and about 10 hours in midwinter. In the southern half of the world the seasons are the opposite.