A plot of the declination of the sun (assuming a latitude of 50° N) for a year is shown below. I apologize for the quality of the graphic, but it proved difficult to get anything good. The scanner copied the original plot to the printer very well, and this graphic is a scan of the copy in PhotoStudio. A scan of the original on green graph paper in PhotoStudio was useless because of Moiré effects, which are observable even in the graphic here.
The plot demostrates that the latitude, and the days of equinox and solstice can be determined with fair accuracy, better than one degree, even from such a simple instrument. Making the observations kept me aware of the movements of the sun, which was very instructive and satisfying. The curve resembles a sine curve, but it is not, of course.
Return to Gnomon
Composed by J. B. Calvert
Last revised 3 September 1999