EFFECT OF UNEQUAL DAYS AND NIGHTS ON TEMPERATURE
The inequality in the length of the days in different parts of the year, occasioned by the inclination of the Earth’s axis, is of itself sufficient to produce a marked variation in temperature.
During the day the Earth receives from the Sun more heat than it radiates into space; while during the night it radiates more than it receives. Hence a succession of long days and short nights results in an accumulation of heat, raising the average temperature and producing summer; while long nights and short days result in a temperature below the average, producing winter.
Again, the heating power of the Sun in each hemisphere is greatest at the period of the longest days, because of its greater altitude in the heavens; and least at the period of shortest days. Thus long days and a high sun operate together to produce the high temperature of summer; while long nights and a low sun cause the low temperature of winter.
The following table gives the length of the longest day, excluding the time of twilight, and of the shortest night, in the different latitudes, with the difference of duration in hours and minutes, thus exhibiting more clearly the above law.
=============+=============+================+============ =LATITUDE= |=Longest Day=|=Shortest Night=|=Difference= -------------+-------------+----------------+------------ Equator | 12.0 hours | 12.0 hours | 00.0 hours 10° | 12.7 „ | 11.3 „ | 1.4 „ 20° | 13.3 „ | 10.7 „ | 2.6 „ Tropics | 13.5 „ | 10.5 „ | 3.0 „ 30° | 14.0 „ | 10.0 „ | 4.0 „ 35° | 14.5 „ | 9.5 „ | 5.0 „ 40° | 15.0 „ | 9.0 „ | 6.0 „ 45° | 15.6 „ | 8.4 „ | 7.2 „ 50° | 16.3 „ | 7.7 „ | 8.6 „ 55° | 17.3 „ | 6.7 „ | 10.6 „ 60° | 18.7 „ | 5.3 „ | 13.4 „ Polar Circles| 24.0 „ | 0.0 „ | 24.0 „ 67-1/2° | 1 month | 0.0 „ | ... 69-1/2° | 2 months | 0.0 „ | ... 73.3° | 3 „ | 0.0 „ | ... 78.3° | 4 „ | 0.0 „ | ... 84° | 5 „ | 0.0 „ | ... North Pole | 6 „ | 0.0 „ | ... -------------+-------------+----------------+------------
The inequality of day and night increases slowly in the tropical regions, but more and more rapidly towards the polar circles. Beyond these circles the Sun, in the hemisphere in which it is vertical, makes the entire circuit of the heavens, without sinking below the horizon, for a period varying from twenty-four hours to six months; while in the opposite hemisphere there is a corresponding period of continuous night.