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

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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 ( Heel Boots Black 1TO9 Low Zip High Toe Closed Boots Track Not MNS02586 Lining Rubber Resistant Water Top Warm Womens Floral Suede Urethane i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Floral Suede Rubber Warm Black Urethane Boots Resistant 1TO9 Womens Water Not Low Closed Top High Track Heel MNS02586 Zip Toe Lining Boots i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Lining Floral Boots Rubber Womens Heel Water Boots Zip Closed Low High Suede Not MNS02586 Toe Resistant Top Black Urethane Track Warm 1TO9 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 1TO9 Top Toe Boots High Zip Low MNS02586 Heel Not Urethane Closed Rubber Womens Lining Track Resistant Suede Black Water Warm Floral Boots mean solar longitude: i.e.,


We obtain

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

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

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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

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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.Shoes Gold Tango Womens Salsa Closed Wedding Latin Modern Glitter mesh Toe Dance Meijili Ballrom Evening Dance Shoes CA0x6wqZZ, 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