NOON. 



moment of noon on 15th April, 14th June, 31st August, and 

 25th December, and this takes place every year on the same days, 

 or nearly so. 



Noon does not divide the interval between sunset and sunrise 

 into equal parts, but the moment of the meridional transit of the 

 sun's centre does so very nearly. Now, since this may vary to 

 the extent of 16 minutes and 18 seconds from noon, it follows that 

 the parts into which the day is divided by noon may differ in 

 length to the extent of 32 minutes and 36 seconds. 



64. In all almanacks a column is appropriated to the sun's decli- 

 nation. It is therefore necessary to elucidate this technical term. 



On the days of the equinoxes the sun, at the moment of its 

 meridional transit, has a certain altitude. But for the effect of 

 atmospheric refraction, this altitude, subtracted from ninety 

 degrees, would leave a remainder which would be exactly equal 

 to the latitude of the place. Since astronomers have computed 

 and published tables which show the refraction corresponding to 

 each altitude, the refraction can be found in these tables, and 

 being subtracted from the observed altitude of the sun, will leave 

 a remainder which is its true altitude. 



If the altitude of the sun after the March equinox be observed 

 daily at the moment of its meridional transit, it will be found to 

 exceed that which it had on the day of the equinox by a constantly 

 increasing quantity. This excess, after the effects of refraction 

 have been allowed for in the manner just explained, is called the 

 SUN'S DECLINATION, the sun being said to DECLINE or fall from 

 the position it had in passing the meridian at the equinox ; and 

 since, in this case, it declines from that position towards the visible 

 celestial pole that is, towards the north it is said to have 



NORTHERN DECLINATION. 



The meridional altitude will be found to increase continually 

 until the June solstice, when it will exceed the altitude at the 

 equinox by 23 degrees and 28 minutes. The meridional altitude 

 of the sun having then attained its limit, begins to decrease, and 

 with it, of course, decreases the declination, until at length, at 

 the time of the September equinox, it becomes nothing, the meri- 

 dional altitude being again what it was at the March equinox. 



Now, during all this interval, from March to September, the 

 meridional altitude of the sun is greater than it is at the equinoxes, 

 and the declination is consequently all the time northern. 



But if the same course of observation be continued, it will be 

 found that after the September equinox the meridional altitude 

 will become less, and will be less and less from day to day. The 

 sun will then decline more and more to the south of its position 

 at the equinoxes ; that is, it will have SOUTHERN DECLINATION, 



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