Museum of Ancient Inventions: Chaldean Sundial

Chaldean Sundial, Greece, 320 BCE

The inventions of the hemispherium and the hemicyclium are attributed to Berosus (356-323 BCE), a Chaldean priest and astronomer who brought these types of sundials to Greece. Both dials use the shape of a concave hemisphere, a shape like the inside of a bowl that mimics, in reverse, the apparent dome shape of the sky.

As the sun moved across the sky above, the shadow of the gnomon or pin would trace the reverse of its course through the inscriptions on the curve below. The hemispherium was carved out of a block of stone and its inner surface scored with eleven lines, dividing the hemisphere and the passage of a shadow through the day into twelve equal parts. The pin of the hemispherium cast its shadow from the center of the hemisphere, such that the noon-day sun would have no shadow at all. The hemicyclium functioned on the same principle, but part of the hemisphere was cut away to facilitate the reading of the shadows, and the pin was placed horizontally at the lip of the dial.

Method of Construction

Constructed by: Allison Crawford ’98 and Lei Liu ’98

Our sundial consists of an engraved, concave hemisphere carved into poured concrete, at the center of which is a vertical pin to cast the shadow. To build this sundial we needed to first make a mold into which to pour the concrete, then engrave the hour lines into the dried stone and insert the wooden pin. To build the mold, we planed about eight million pieces of wood, glued these into a large, eight-inch by sixteen-inch block, then shaped this into a hemisphere on a lathe. We attached a small peg to the inner bottom of this mold so there would be a hole for the pin. Next we built a plywood box, put the mold flat-side down in the center of it, and poured the concrete. When it dried, we removed the concrete from the box and the mold from the center and engraved the twelve equally-spaced chords for the hour lines. Finally, we cut an eight-inch length of wooden dowel, sanded it, and placed it into the center hole.

Science Topics
Astronomy, Inventions & Scientists
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Ancient History
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