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Sundial Hour Lines Lay out

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Declination Lines of Sundials

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LAYING OUT THE SUNDIAL HOUR LINES - Page 15

Draw lines through these divisions until they cut the line PR, at Io, 11, 12, and so on. From B draw lines through the points Ito, 11, 12, and so on. These lines will be the required hour lines. To obtain the hours after 6 p.m. draw a line through 6 (136 is the 6 o'clock line) parallel to BD, and cutting B5 at G. For the 7 p.m. line make the distance 67 equal to G6. The 8 p.m. line may be obtained in the same way. To obtain the hours before ro a.m., draw a line through any point on BD, such as O, parallel to B6 (the 6 o'clock line). This line cuts B3 at F, and B4 at 4. From O lay off the distance OC equal to OF; and OA equal to 04. Lines drawn from B through the points C and A will give the g a.m. and 8 a.m. lines. The hour lines applied to the sundial plate, in their proper position, and the way in which they should be numbered. Hour Limitations The length of time the sun shines on this sundial and the number of hour lines to be inscribed is governed by the declination. A simple method of determining what hour lines should appear on a declining sundial, where great accuracy is not desired, is by converting the declination from degrees to hours and minutes. One hour of time is equal to 15°. Therefore in the above example, 28° is just a little less than two, hours. Thus, the sun would not shine on this sundial until about 8 a.m. nor would the sun cease to shine on it until about 8 p.m. It must be remembered that this is not an accurate method, for the latitude and time of year should be considered where extreme accuracy is desired. The 12 o'clock line is always a vertical line.

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