The New Student's Reference Work/Seasons

Seasons(sē′z’nz). The motions of the earth on which the seasons depend are explained in Earth. The chief cause of the greater heat of summer and the greater cold of winter is that the sun's rays fall more obliquely on the earth's surface in the latter season than in the former. Another cause is the greater length of the day in summer and of the night in winter. In the tropics the sun's rays always are so nearly direct that no one part of the year is sensibly colder than another. But the zone of calms, in which the rainfall is almost continuous, moves northward with the sun in the northern summer and southward in the southern summer. As the wet zone follows the sun, the regions it crosses have wet and dry seasons. In the arctic and antarctic regions spring and autumn are very short, the year dividing itself simply into a long winter and a short summer. In temperate regions the year is naturally divided into spring, summer, autumn and winter. The almanacs assume that spring begins at the vernal equinox, March 20; summer at the summer solstice, June 21; autumn at the autumnal equinox, Sept. 21; and winter at the winter solstice, Dec. 21. However, the greatest heat is reached sometime after the summer solstice, the time when the sun's rays are most nearly vertical and the day is longest. In like manner the greatest cold of winter comes after the winter solstice the time when the day is shortest and the sun's rays most oblique. The reason in the former case is that, as summer comes on, the earth itself becomes more heated; in the latter, that it keeps a part of the heat which it had got in summer, just as the warmest part of the day is a little after midday and the coldest part of the night is toward morning.