JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. IV OCTOBER 4, 1914 No. 16 



ASTRONOMY. — Condensation of the tables of the azimuth of 

 celestial bodies. G. W. Littlehales, Hydrographic Office. 



If finding the azimuth be viewed as a terrestrial measurement 

 in connection with which the observed celestial body is considered 

 to be projected vertically downward on the surface of the earth^ 

 that is to say, if the azimuth-angle be regarded as the angle whose 

 apex is formed at the geographical position of the observer 

 between his meridian and the great-circle arc passing through 

 his geographical position and the geographical position of the , 

 observed celestial body, then it will become commonplace to 

 regard any value of the azimuth as applying not only to the 

 position of the particular celestial body observed but as apply- 

 ing besides to all geographical positions of which the great-circle 

 passing through the geographical position of the observer and 

 the geographical position of the observed celestial body is the 

 locus; and, since every great-circle of the earth, except the equator 

 itself, crosses the equator, there is always a point on the equator 

 whose azimuth or true bearing from the observer is the same as 

 the azimuth of the observed celestial body. The fact that this 

 relation exists gives rise to the suggestion that the tables of the 

 azimuths of celestial bodies at present in use, giving values for 

 each latitude of the observer throughout a wide range of de- 

 clination of the observed body, could be reduced in volume to 

 the extent of omitting all except what relates to 0° of declination, 

 provided only that convenient means be supplied for finding 

 the difference of longitude or hour-angle between the meridian 



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