Timber sundial by Renold M Sequeira, image Nick Lomb
This little timber sundial is an equatorial type. The central gnomon that casts the shadow is set up so that it points north and south with the higher end towards the south celestial pole (in the southern hemisphere). The semi-circular ring, which is marked with the hours at an even spacing, is then in the plane of the Earth’s equator. The dial is read by looking at the shadow of the edge of the gnomon on the ring.
This is a popular type of sundial for large public dials and there are famous examples such as by the English sculptor Henry Moore in Chicago, outside the Adler planetarium.
The little timber sundial was brought into Sydney Observatory by a visiting sculptor in wood from the Indian state of Maharashtra, Renold M Sequeira. Mr Sequeira says that it is a small-scale replica of the giant sundial in Jaipur India. The Jaipur sundial is indeed giant as it has a width of over 20 metres. A sundial of that size should be highly accurate as there is room for very precise time markings on the semi-circular dial. However, as the distance from the gnomon to the dial increases the edge of the shadow becomes fuzzier and harder to read with precision.
I am unsure of the weather resistance of the little timber sundial, but it is a nice piece and will have educational uses at Sydney Observatory. Thank you Mr Sequeira.