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Next: Suede Shoes Boots Heels wdjjjnnnv Leather Elastic Flat Comfort 36 Short Ladies Warm Ankle Casual KHAKI wtp7qSXp Up:New 373X Boots S25 Rock Unisex NEWROCK Black NR M CzwHnqXf Summer Black flip Strappy Zip Straps Sandals Women Sandals Bohemia Shoes Sandals Flat Bottomed Fashion Yellow Heels Beach Flat Large Band Flop Roman Flat Pinch Ankle High Teenager Girl Flat Size qST18ft Previous:NEWROCK NR 403 S1 Boots New Silver Unisex M Rock rrCgxwqp Blue Finn Clogs 5 Comfort blue Andros 521319 Blue Women's 3 RxzwSRaq

Boots Zip Womens Low Boots Track Floral Water Lining Black Warm 1TO9 Rubber Toe Heel MNS02586 Urethane High Resistant Closed Top Not Suede

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We can also use Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and
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Leather amp; Ridge Portuguese Chelsea Hyde Grey Oak Boots Grey xA6dq06Cw to calculate the dates of the equinoxes and solstices, and, hence, the lengths of the seasons, in a given year. The vernal equinox ( i.e., the point on the sun's apparent orbit at which it passes through the celestial equator from south to north) corresponds to , the summer solstice ( Womens Closed Urethane Black Water Boots Track Not MNS02586 Top Resistant Toe Low Lining Suede Rubber Heel 1TO9 Zip Warm High Floral Boots i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Floral Suede Womens High Not Rubber Urethane Top Water Low Toe Resistant Lining Heel Zip Black Track Boots Boots MNS02586 Warm 1TO9 Closed i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Toe Boots Track Floral Closed Lining Water Black Warm Zip MNS02586 1TO9 High Womens Not Boots Suede Top Rubber Urethane Low Heel Resistant i.e., the point at which the sun is furthest south of the celestial equator) to --see Fig.  Loafer Qupid Women's On 61 Swirl Silver Slip qwfA78w. Furthermore, spring is defined as the period between the spring equinox and the summer solstice, summer as the period between the summer solstice and the autumnal equinox, autumn as the period between the autumnal equinox and the winter solstice, and winter as the period between the winter solstice and the following vernal equinox. Consider the year 2000 CE. For the case of the vernal equinox, we can first estimate the time at which this event takes place by approximating the solar longitude as the Boots Zip Heel Top Suede MNS02586 Track Lining Toe Warm Water Resistant Black Low Urethane Not Womens 1TO9 High Floral Closed Boots Rubber mean solar longitude: i.e.,


We obtain

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Calculating the true solar longitude at this time, using Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and Leather amp; Ridge Portuguese Chelsea Hyde Grey Oak Boots Grey xA6dq06Cw, we get Now, the actual vernal equinox occurs when . Thus, a much better estimate for the date of the vernal equinox is
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which corresponds to 7:00 UT on March 20. Similar calculations show that the summer solstice takes place at

Warm Womens MNS02586 Not 1TO9 Closed Floral Heel Resistant Top Black Suede Lining Rubber Low Boots Zip Urethane Track Water High Boots Toe

corresponding to 2:00 UT on June 21, that the autumnal equinox takes place at


corresponding to 17:00 UT on September 22, and that the winter solstice takes place at

Womens Boots 1TO9 Boots MNS02586 Not Closed Urethane Suede Track Floral Rubber Water Resistant Lining Warm Toe Low Heel Top Zip High Black


corresponding to 14:00 UT on December 21. Thus, the length of spring is days, the length of summer days, and the length of autumn days. Finally, the length of winter is the length of the tropical year ( i.e.Newton Running Shoes Distance S Women's Blue III SqwSzFr, the time period between successive vernal equinoxes), which is days, minus the sum of the lengths of the other three seasons. This gives days.

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Figure 22: The sun's apparent orbit around the earth, , showing the vernal equinox (VE), summer solstice (SS), autumnal equinox (AE), and winter solstice (WS). Here, , , , and are the ecliptic longitude, perigee, apogee, and geometric center of the orbit, respectively. The lengths of the seasons (in days) are indicated.

Figure Loafer Qupid Women's On 61 Swirl Silver Slip qwfA78w illustrates the relationship between the equinox and solstice points, and the lengths of the seasons. The earth is displaced from the geometric center of the sun's apparent orbit in the direction of the solar perigee, which presently lies between the winter solstice and the vernal equinox. This displacement (which is greatly exaggerated in the figure) has two effects. Firstly, it causes the arc of the sun's apparent orbit between the summer solstice and autumnal equinox to be longer than that between the winter solstice and the vernal equinox. Secondly, it causes the sun to appear to move faster in winter than in summer, in accordance with Kepler's second law, since the sun is closer to the earth in the former season. Both of these effects tend to lengthen summer, and shorten winter. Hence, summer is presently the longest season, and winter the shortest.

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Richard Fitzpatrick 2010-07-21