BC Gnomonics

The analemma of vitruvius is a two dimensional model of the celestial sphere. With an understanding of its components, the user is able to model the position of the sun for any given moment, at any latitude. By projecting the sun's rays through a nodus, the corresponding shadows can be drawn in either two or three dimensions.

 

Through sequences of graphical steps, the figure can be used to draw a multitude of stationary and portable sundials, laying out modern, seasonal, Babylonian, or Italian hour lines.

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The analemma can be imagined as a side-view of the celestial sphere. Because of the limitations of this vantage point, the western halves of the sun's daily arcs are folded into the plane of the drawing.