SEASON OF THE YEAR AND DAY LENGTH IS DETERMINED BY  THE POSITION OF THE EARTH RELATIVE TO THE SUN  As the earth revolves around the sun, its axis points to the same location in space. At the summer solstice the axis is tilted 23 1/2 degrees towards the sun. This causes long days and short nights. At the winter solstice the axis is tilted 23 1/2 degrees away from the sun. This causes short days and long nights. At the autumnal and vernal equinox, the axis is not pointed towards or away from the sun. (I call it obliquely parallel, or cock-eyed parallel) This causes equal days and nights.