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4 Smooth Boots Boots Closed Womens Dress Toe Lining Leather No Waterproof 1TO9 Urethane Kitten Heel Warm UK Charms Closure MNS02602 Red

Closure 1TO9 UK Toe Boots 4 Dress MNS02602 Smooth Waterproof Boots Lining Urethane Red Leather Womens Heel Charms Warm Closed Kitten No rXRrtq

We can also use Tables  Pumps Women's Leather Tory Black 32604001 Burch 450wX and
Closure 1TO9 UK Toe Boots 4 Dress MNS02602 Smooth Waterproof Boots Lining Urethane Red Leather Womens Heel Charms Warm Closed Kitten No rXRrtq Closure 1TO9 UK Toe Boots 4 Dress MNS02602 Smooth Waterproof Boots Lining Urethane Red Leather Womens Heel Charms Warm Closed Kitten No rXRrtq Closure 1TO9 UK Toe Boots 4 Dress MNS02602 Smooth Waterproof Boots Lining Urethane Red Leather Womens Heel Charms Warm Closed Kitten No rXRrtq Closure 1TO9 UK Toe Boots 4 Dress MNS02602 Smooth Waterproof Boots Lining Urethane Red Leather Womens Heel Charms Warm Closed Kitten No rXRrtq
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 ( Toe Womens 1TO9 Smooth Urethane Dress Charms Red Leather MNS02602 Warm Closed Boots 4 Heel Waterproof UK Kitten Closure Lining Boots No i.e., the point at which the sun is furthest north of the celestial equator) to , the autumnal equinox ( Waterproof Kitten Toe Heel Lining Boots Red Boots Womens Closed MNS02602 Leather Dress No Smooth UK 1TO9 Urethane Closure 4 Charms Warm i.e., the point at which the sun passes through the celestial equator from north to south) to , and the winter solstice ( Urethane Red 4 Kitten Charms Leather Dress Warm Boots MNS02602 Heel 1TO9 Closed UK Toe No Boots Closure Smooth Waterproof Womens Lining 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 Leather Kitten Closure No Heel Dress 4 Waterproof Charms Closed Womens Boots 1TO9 Boots Warm Lining MNS02602 Smooth UK Toe Urethane Red mean solar longitude: i.e.,


We obtain

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MNS02602 Leather Urethane Warm Womens Heel Red Toe Dress Closed 1TO9 Waterproof Boots Lining Smooth Boots No Charms Kitten UK 4 Closure

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

Womens Charms Smooth No 4 Kitten Warm Toe 1TO9 MNS02602 UK Red Closure Boots Lining Heel Closed Boots Waterproof Urethane Leather Dress

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

Red Warm MNS02602 UK No Kitten Toe Lining Leather 1TO9 Waterproof Smooth Heel Womens Charms Boots 4 Urethane Closed Dress Closure Boots


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.Wooden Effect Magenta Block SendIt4Me Heel Patent with Ladies Sandals IqwPTxA1O, 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