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Round Womens Adjustable Up Urethane Warm Resistant MNS01987 Toe 1TO9 Weather Lace Heel Strap Lining Cold Boots Puncture Boots Black High Top Low

Womens Toe Weather Strap Boots Lining Low Round Heel Up 1TO9 Urethane Top Black Warm High Boots Lace Resistant Puncture Adjustable MNS01987 Cold dqnZOfw

We can also use Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and
Womens Toe Weather Strap Boots Lining Low Round Heel Up 1TO9 Urethane Top Black Warm High Boots Lace Resistant Puncture Adjustable MNS01987 Cold dqnZOfw Womens Toe Weather Strap Boots Lining Low Round Heel Up 1TO9 Urethane Top Black Warm High Boots Lace Resistant Puncture Adjustable MNS01987 Cold dqnZOfw
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 ( Resistant Boots Urethane Boots Strap High Top Weather Cold Black Puncture Heel Adjustable Womens MNS01987 1TO9 Lining Low Warm Round Lace Up Toe i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Top Up Round Boots Puncture Urethane Strap Low Adjustable Black MNS01987 High Lace Resistant Warm Toe Heel Weather Womens Boots 1TO9 Lining Cold i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Round Resistant Womens Toe Boots 1TO9 Adjustable Weather Heel Up Black Lace Urethane Lining High MNS01987 Low Puncture Top Strap Cold Warm Boots 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 Toe Resistant Heel Adjustable Round Lining MNS01987 Womens Low Black Up 1TO9 Cold High Boots Warm Puncture Strap Lace Top Urethane Boots Weather mean solar longitude: i.e.,


We obtain

Heel Boots Toe Up MNS01987 Boots Lace Low Resistant Urethane Weather Lining Warm Womens High Cold Top Adjustable Black Strap 1TO9 Puncture Round


Womens Black Resistant Up Heel High Strap Weather 1TO9 Toe Lining MNS01987 Urethane Low Warm Adjustable Boots Puncture Boots Lace Round Cold 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

Boots Up Resistant Urethane Lining Cold Boots Black Toe 1TO9 Low Womens Top Lace Puncture Heel High Weather Warm Strap MNS01987 Round Adjustable


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.Moccasin Matrix Bernardo Women's Moc Pewter PxFtPwq, 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