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Hello, I'm Milo for About.com, and today we are talking about the four seasons.Since the Earth is not only rotating around the sun on a yearly cycle but is tilted on its axis relative to the solar-Earth plane at 23.5 degrees, the sun's rays strike the Earth at different points causing temperatures and daylight to change cyclically as well.  We call these cyclical changes seasons. They are spring, summer, autumn, and winter. These cycles in the Earth's temperature and daylight are more distinct in certain parts of the earth. These places are near two important latitudes, the Tropic of Cancer and the Tropic of Capricorn. So obviously these changes in the seasons do not happen simultaneously in the northern and southern hemispheres.  Actually, seasons in the northern hemisphere occur at opposite times of the year than in the southern hemisphere. The solstices and the equinoxes are connected with the seasons, as the seasons begin at the time of the solstice or equinox. The solstices occur around June 21 and December 20 but not necessarily exactly on those dates. They are known as the June and December solstice and each one marks the beginning of the winter or summer season, depending on whether you are in the Northern or Southern Hemisphere. During the solstices the rotation of the Earth brings it to the peak of the Sun's rays, hitting either the Tropic of Cancer in the northern hemisphere, or the Tropic of Capricorn in the southern hemisphere. At this peak the Earth's rotation and tilt begins to move the Sun's rays back in the other direction, towards the equator and beyond. During the June solstice the rays of the sun hit the Tropic of Cancer directly.  During the December solstice the Sun's rays hit the Tropic of Capricorn directly.  People living near those lines on the globe will be in summer during those times, and people living in the opposite lines will be in winter. The equinoxes occur around March 21 and September 21 but not necessarily exactly on those dates. During the equinoxes the rotation and tilt of the Earth causes the Sun's rays to hit the equator directly. These times mark the middle, more or less, of the Earth's rotation between the solstices as it moves the Sun's rays towards the next peak mentioned before. The Vernal Equinox marks the beginning of spring and the Autumnal Equinox the beginning of autumn. For more excellent and helpful information on practically anything, check us out at About.com.
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