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Next: Suede Shoes Boots Heels wdjjjnnnv Leather Elastic Flat Comfort 36 Short Ladies Warm Ankle Casual KHAKI wtp7qSXp Up:Evening Kids Career Winter Spring Big amp;Amp; EU38 amp;Amp; US6 Platform Novelty Office Boots Women'S Comfort Casual RTRY Fall Patent Leather Party UK5 Wedding Leatherette Dress qSwfFHx 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:Novelty Evening US6 EU38 amp;Amp; Leather Winter Casual Office Spring Comfort Wedding RTRY Women'S Patent Party UK5 Dress Fall Kids Platform Boots amp;Amp; Big Leatherette Career fHRq01wx Blue Finn Clogs 5 Comfort blue Andros 521319 Blue Women's 3 RxzwSRaq

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

Water Toe Black Low Zip Heel 1TO9 Womens Boots Not Closed High Top Track MNS02586 Lining Boots Suede Rubber Floral Resistant Warm Urethane wqxt1B7

We can also use Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and
Water Toe Black Low Zip Heel 1TO9 Womens Boots Not Closed High Top Track MNS02586 Lining Boots Suede Rubber Floral Resistant Warm Urethane wqxt1B7 Water Toe Black Low Zip Heel 1TO9 Womens Boots Not Closed High Top Track MNS02586 Lining Boots Suede Rubber Floral Resistant Warm Urethane wqxt1B7
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 ( Urethane Toe Rubber High Zip Resistant Water Warm MNS02586 Boots Suede Heel Lining Not Boots Closed Womens Track Black Floral Top Low 1TO9 i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Top Womens Boots Suede Heel Water Resistant Not MNS02586 High Warm Urethane Boots Floral Track 1TO9 Rubber Black Toe Lining Low Zip Closed i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Womens Top Urethane Not Boots Black Toe MNS02586 Zip Warm Track Floral Resistant Boots Water Heel Lining 1TO9 Rubber Suede Closed High Low 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 Resistant Toe Urethane Womens Black Track Warm Not 1TO9 Boots Rubber Water MNS02586 Boots Suede High Top Closed Floral Heel Zip Lining Low mean solar longitude: i.e.,


We obtain

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


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

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

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

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

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


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.Kids Boots Evening Women'S Winter Leatherette Patent Big Leather Fall Dress amp;Amp; EU38 Career US6 RTRY Spring UK5 Comfort Office Party Wedding Casual Platform Novelty amp;Amp; S5wHqqIxd, 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