The four seasons arise because the Earth is tilted at an angle of approximately 23.5 degrees. The tilt of the planet is known to fluctuate very slightly over long periods of time as a result of the complex motion of the Earth and moon. During the summer months the intensity of the sunrays hitting the Earth is greater than in the winter. An easy way to visualize this is by shining a flashlight directly (perpendicularly) onto a flat surface. It will brightly illuminate a small circle. When the surface is tilted, the area illuminated becomes larger and oval, and the brightness at any particular location is diminished, particularly at the far edge which would be representative of the northern, cooler regions on Earth. As the Earth follows its elliptical orbit around the sun, the tilt of it remains essentially constant. Therefore the intensity of sunlight hitting regions north and south of the equator will vary causing the seasons.
The Equator is the imaginary line that divides the Earth into the northern and southern hemispheres. The equinox occurs at the point in Earth’s orbit when the sun’s rays are directly perpendicular to the Equator. At this time, when you look to the sky at noon, the sun will appear directly overhead at its zenith. This happens twice a year: the first day of fall (September 21st) and the first day of spring (March 21st).
The Tropic of Cancer and the Tropic of Capricorn are two other imaginary lines drawn around the planet and are located at the latitude of 23.5 degrees north and south of the Equator, respectively. They are defined by the tilt of the Earth. At the summer solstice of June 21st, the sun shines directly overhead at the Tropic of Cancer. This not only marks the beginning of summer in the northern hemisphere, but it is also the longest day of the year. The winter solstice for the northern hemisphere occurs on December 21st and marks the shortest day of the year. In the northern hemisphere, during the months surrounding the summer solstice, the sun rises toward the northeast and sets toward the northwest. This shifts to the southeast and southwest around the winter solstice.
The Arctic and Antarctic circles are the last two of the five imaginary lines or major circles of latitude marking the globe and run 66.56 degrees north and south of the equator, respectively. In the northern hemisphere, the region north of this circle is known as the Arctic. In this region the sun is above the horizon for at least one entire day per year (land of the midnight sun) around the summer solstice. Around the winter solstice, the sun is below the horizon for at least one entire day per year.
The five major circles of latitude do move slightly as a result of the tilt of the Earth fluctuating. Because of this, the exact date and time of the equinox and solstices vary from year to year. The time of the summer solstice for 2012 is June 20th at 11:09 p.m. Interestingly, if the Earth were completely upright, there would be no Tropics, Arctic or Antarctic. At the equator the sun would always rise in the east, pass directly overhead at noon, and set in the west. In the Arctic and Antarctic, the sun would just circle the horizon. There would be no seasons.
Stonehenge – This ancient stone monument is believed to have been constructed anywhere from 3000 B.C. to 2000 B.C. and is located in the British county of Wiltshire. The northeast opening of the monument precisely matches the direction of the summer solstice sunrise and the winter solstice sunset of that period. On June 21st, the rising sun shines its light in between the Heel Stone onto the Alter Stone and the center of the horseshoe.
Temple of Kukulcan – Located in Chichen Itza, Mexico, the Temple dates back to between 300 and 450 A.D. On the summer solstice, the northern side of the Temple is fully illuminated by the sun, while the southern and westerly sides are shaded by the temple itself. From the air it appears as though the temple has been divided in half by the sun’s rays in a perfect diagonal line. Even more astounding is what occurs at the spring and fall equinoxes, where a shadow resembling a snake slithers down the stairs on the northern face. When it reaches the bottom, two stone serpent heads become illuminated.
Mesa Verde National Park – Located in northwestern New Mexico, the Chaco Canyon was once home to the ancient Chacoan civilization. Examination of the ruins in the area revealed a structure that what was once known as the Community House, but has since been renamed the Sun Temple. It was renamed as the front wall of the Temple is aligned to the summer solstice sunrise and the winter solstice sunset.
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Author of Science Fiction Thrillers, SPECTRA and ENTITY