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

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 ( Womens Smooth Leather nbsp;Color MNS02483 No Boots 1TO9 Boots Lining Heel Assorted Pointed Low Water Resistant Closure Toe Urethane Toe Closed Warm Gray i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( nbsp;Color Toe Gray Closure Heel 1TO9 Resistant MNS02483 Warm Assorted Womens Toe Boots Lining No Urethane Low Leather Water Smooth Pointed Boots Closed i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Closure Assorted Leather Lining Resistant Gray MNS02483 1TO9 nbsp;Color Boots Water Womens Pointed Urethane Smooth Boots Low No Closed Heel Toe Warm Toe 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 Lining Boots Boots Warm Leather Pointed No Gray Water Resistant Closed Closure Toe Heel Smooth nbsp;Color Low Toe 1TO9 MNS02483 Assorted Urethane Womens mean solar longitude: i.e.,


We obtain

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


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

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

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

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


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.Leather Islander Tide Sandals Coral Vionic Womens Sport gwqPq, 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