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DECLINATION LINES OF SUNDIALS - Page 9

The line of declination for December 22 cuts the horizontal line between 7 and 8 a.m., and a little before 7:30 a.m., Apparent Time. Thus, on December 22nd the sun will rise shortly before 7:30 a.m. According to an almanac computed for latitude 400N, the sun will rise at 7:20 a.m., Apparent Time, on December 22nd. The appearance of the lines of declination on a polar sundial. The construction of the lines is the same as for the east sundial. The horizontal line for this sundial has not been shown, owing to the very short period of time over which it could be used. It may be inscribed in the same manner as for the equatorial sundial, Plate XI. LINES OF DECLINATION ON THE ARMILLARY If reference is made to the plate on page 126 the method of inscribing the lines of declination on the armillary will be apparent. The sphere represents the plan of the heavens with the earth at its center. Therefore the nodus should be placed at the exact center of the sphere. The lines of declination will be straight lines, parallel to the plane of the equator; and in-scribed on the inner surface of the circle representing the equator. The equatorial band should be wide enough to accommodate the lines noting the greatest northern and southern declination of the sun. The horizontal line may be determined in the same manner as for the equatorial sundial. There is another method of plotting the lines of declination, which employs tables showing the altitude of the sun. This will no doubt appeal to those who have access to such tables. The most satisfactory tables are those published by the U.S. Hydrographic Office, designated as No. 201 and No. 203. These tables show the altitude and azimuth of celestial bodies for stated values of declination and latitude, and they will be found very useful when constructing a sundial.

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