The Earth revolves around the Sun. The sunlight reaches the Earth at an angle. On each day of the year, the sun will be perpendicular at a given latitude. At the start of spring and at the start of autumn it passes over the equator. On the June Solstice it is over the Tropic of Cancer, at 23.5 degrees north. In the Northern Hemisphere this is the longest day of the year, which has the shortest night and is called the Summer Solstice. In the Southern Hemisphere this is the shortest day of the year, which has the longest night and is called the Winter Solstice. On the December Solstice it is over the Tropic of Capricorn, at 23.5 degrees south. In the Southern Hemisphere this is the longest day of the year, which has the shortest night and is called the Summer Solstice. In the Northern Hemisphere this is the shortest day of the year, which has the longest night and is called the Winter Solstice.