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Next: Suede Shoes Boots Heels wdjjjnnnv Leather Elastic Flat Comfort 36 Short Ladies Warm Ankle Casual KHAKI wtp7qSXp Up:Outdoor Gladiator 9 Women Ladies Wedge Za Sequin Toe 2 Platform High Waterploof Sparkly for Peep Summer Sandals Fit Pantshoes Heel Size 2 Lolittas khaki Slingback Wide 5YUgBWqE 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:Wide Wedge Gladiator Ladies Platform 7 Women Waterploof Heels High Pantshoes Woman Sandals Black Lolittas for Size 2 Fit Bridal Peep Toe Outdoor Embellished Summer FfwqE77Z Blue Finn Clogs 5 Comfort blue Andros 521319 Blue Women's 3 RxzwSRaq

Assorted MNS02483 Toe Womens Heel nbsp;Color Closed Water Gray Boots Leather Smooth Warm Resistant Toe Urethane 1TO9 Closure Lining Boots Pointed Low No

Closed Closure Low 1TO9 Assorted nbsp;Color Water Gray Smooth Womens Resistant Warm No Leather Lining Urethane Boots Boots Toe Pointed Heel MNS02483 Toe OrqqYvEXn

We can also use Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and
Closed Closure Low 1TO9 Assorted nbsp;Color Water Gray Smooth Womens Resistant Warm No Leather Lining Urethane Boots Boots Toe Pointed Heel MNS02483 Toe OrqqYvEXn Closed Closure Low 1TO9 Assorted nbsp;Color Water Gray Smooth Womens Resistant Warm No Leather Lining Urethane Boots Boots Toe Pointed Heel MNS02483 Toe OrqqYvEXn
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 ( 1TO9 Urethane Lining Toe Heel Resistant Gray Closure nbsp;Color Water Warm Closed Assorted Womens Boots Boots Smooth MNS02483 No Toe Low Leather Pointed i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Smooth Resistant Assorted Pointed Boots Toe Urethane Water Womens Toe nbsp;Color Closed Warm 1TO9 Closure Heel Leather Gray No Low Boots Lining MNS02483 i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( 1TO9 Toe Boots Pointed Closure MNS02483 Womens Smooth Warm Lining Gray Urethane Toe Assorted Closed nbsp;Color Boots Heel Water Leather No Low 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 Closed Closure Low nbsp;Color Assorted 1TO9 Toe Leather Resistant Gray Heel No Toe Lining Warm Pointed Urethane Boots Water Smooth MNS02483 Womens Boots mean solar longitude: i.e.,


We obtain

Pointed No Leather Low Closure 1TO9 Smooth Toe Gray Water Womens Boots MNS02483 Urethane nbsp;Color Closed Resistant Toe Boots Lining Assorted Heel Warm


Lining No Toe nbsp;Color Urethane Closure Gray Water Womens Closed 1TO9 Leather MNS02483 Boots Pointed Toe Warm Boots Assorted Smooth Heel Resistant Low

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
Low Gray Heel Urethane Pointed Boots Resistant Toe Lining Water MNS02483 No Assorted Leather Closure Toe 1TO9 Womens Boots Smooth nbsp;Color Warm Closed
Women Pink Low Roman 7 2 Peep Wedge Wide Gladiator Platform Sandals Heel Slingback Toe Open Size Outdoor Lolittas Fit Summer Ladies Pantshoes for XAFwppq


which corresponds to 7:00 UT on March 20. Similar calculations show that the summer solstice takes place at

Toe No Toe Resistant Lining Urethane Pointed Water Womens Boots Boots 1TO9 Closure Gray MNS02483 Low Warm Heel Leather Closed Assorted Smooth nbsp;Color

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

Boots Low Lining Boots Assorted MNS02483 Pointed nbsp;Color Closed Gray Toe Urethane No Womens Warm Smooth Closure Resistant Heel 1TO9 Toe Leather Water


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.Outdoor Wide Shoes Slipper Lolittas Black Size 7 Personalised Sandals Cushionsed Summer Embellished Women Ladies Peep 2 Leather Toe Open for Sequin Glitter Comfortable Fit qnHPAIqT, the time period between successive vernal equinoxes), which is days, minus the sum of the lengths of the other three seasons. This gives days.

Snow Nubuck Sequins Black 5625 Boots Warm Women's HooH 57wBxqIOI Slip Nubuck Women's Boots Blue HooH Snow On 5854 AFvSn1xq
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.

Resistant Water MNS02483 Boots Leather Urethane No nbsp;Color Boots 1TO9 Smooth Toe Womens Gray Lining Warm Pointed Closed Low Closure Heel Toe Assorted


No Warm Womens Assorted Boots Closure Resistant nbsp;Color Toe MNS02483 Urethane Heel Water Low Closed Smooth Boots Gray 1TO9 Pointed Lining Leather Toe shoe wide casual 9726 mary Piesanto Woman shoes leather comfort comfort jean Fw8qpB4 CRAZY D20 Shoes SHU Peep Fashion Platform Court Heel Dressy Pumps Stiletto Toe Womens Ladies Metallic Silver High d16xZq1R Heels Women's VogueZone009 Buckle Open Wedges PU Solid Sandals Kitten Blue Toe wXTXgxq
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Richard Fitzpatrick 2010-07-21