Armillary sphere sundial

Rock Garden Lawn

Located beside the Main Path near the Rock Garden, beside a spacious lawn, is a fine example of an armillary sphere sundial. Made from silicon bronze, the sphere is 0.5m in diameter, and is mounted on a rock for easy reading. An adjacent plaque gives the time correction needed and instructions for reading the sundial. The precise geographic coordinates for the dial are Latitude 35° 16' 45" S, Longitude 149° 06' 26" E.

The dial was presented by the Friends of the Australian National Botanic Gardens in November 1999 and was made and installed by Sundials Australia in Adelaide. The dial is shown on the Visitor Guide map of the Gardens and is about 300m north of the Visitor Centre. The walk to the summit of Black Mountain starts nearby.

Armillary sphere sundials, modeled on the celestial or terrestrial sphere, are constructed from three or more interlocking rings which provide support for the rod-like gnomon, which forms the axis of the sphere, and casts the time-telling shadow on the equatorial ring. In the case of the ANBG sundial this equatorial ring interlocks with a meridian and polar ring.

The equatorial ring carries hour lines marked at 10 minute intervals from 5a.m. to 7 p.m., the approximate time (Australian Eastern Standard Time) of earliest sunrise and latest sunset respectively in Canberra. The gnomon is set at an angle of 35° to the horizontal (corresponding to the latitude of Canberra) so that its upper end points at the South Celestial Pole.

Another fine armillary sphere in Canberra can be seen in the north corner of Parliament Drive outside Parliament House.

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