154 



PRACTICAL ASTRONOMY 

 TABLE (Continued) 



the sun is observed; its values for different altitudes are given 



in the accompanying table. It is additive. 



4. The correction for semi-diameter is also necessary when 



the sun is observed, owing to the fact that either the upper 



or the lower edge of the disk, instead of the center, is observed. 



This correction may be taken from the Ephemeris in the same 



manner as the sun's declination. For the purpose of ordinary 



calculations, however, this may be taken from the following 



table: 



Time of year (approx.) . .Jan. 1, Apr. 1, July 1, Oct. 1 



Sun's semi-diameter 16' 18" 16' 2" 15' 45" 16' 2" 



It is additive when the lower limb is observed, and subtrac- 



tive when the upper one is observed. 



Corrections for Observation of the Sun for Azimuth. When 



the sun is observed for azimuth, a correction for semi-diameter 



