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The summer solstice occurs at the moment the earth's tilt toward from the sun is at a maximum. Therefore, on the day of the summer solstice, the sun appears at its highest elevation with a noontime position that changes very little for several days before and after the summer solstice. In fact, the word solstice comes from Latin solstitium or sol (the sun) + -stit-, -stes (standing). The summer solstice occurs when the sun is directly over the Tropic of Cancer, which is located at 23.5° latitude North, and runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India, and southern China. The sun will be directly over the Tropic of Cancer at 1116 am MDT on June 21, 2011. For every place north of the Tropic of Cancer, the sun is at its highest point in the sky and this is the longest day of the year.

There are two times of the year when the Earth's axis is tilted neither toward nor away from the sun, resulting in an equal amount of daylight and darkness at all latitudes. These events are referred to as equinoxes and occur near March 21 (Vernal Equinox) and near September 21 (Autumnal Equinox). At the equator, the sun is directly overhead at noon on the two equinoxes. The Vernal Equinox occurred at 521 pm MDT on March 21, 2011. The Autumnal Equinox will occur at 304 am MDT on September 2, 2011.

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