Length of Day

the interval of time between sunrise and sunset, during which the sun is above the horizon. The length of day depends upon the geographic latitude of a place and upon the inclination of the sun. At the equator, the length of day is constant and equals 12 hours. In the northern hemisphere, the length of day is more than 12 hours during the positive inclination of the sun (that is, in the spring and summer) and less than 12 hours during the negative inclination of the sun (in the autumn and winter). At the equinoxes (spring and autumn), the day equals the night (if one does not consider refraction) everywhere on the earth. The longest day is the summer solstice and the shortest is the winter solstice. Within the polar circles, the length of day in the summer can exceed 24 hours (the polar day), and at the poles daytime lasts six months.