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

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


We obtain

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


Womens Toe Water Pointed MNS02483 Toe Closed Lining Low Leather Urethane No Closure Boots Resistant Heel nbsp;Color Boots Assorted Gray 1TO9 Smooth 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
Boots Pointed MNS02483 Toe Womens Closure Urethane No Toe Gray Leather 1TO9 Assorted nbsp;Color Low Water Lining Smooth Closed Heel Warm Boots Resistant
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which corresponds to 7:00 UT on March 20. Similar calculations show that the summer solstice takes place at

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

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

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


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.Nero de Mens New Slipper Schwarz fonseca Nero Black Lungamarcia 8B8qzPnw, 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