Article of the month October

Armillary sphere sundial with auxiliary scales

Several examples of armillary spheres with auxiliary scales exist in The Netherlands.
The specimen shown here is in the garden of Twickel Manor in Delden, Overijssel province.

The sundial sits on a splendid pedestal, the pair really fitting the lush manor gardens.
On top of the large armillary there is a second.

Remarkable are the scales on the outside of the equatorial band, which act as auxiliary sundials.
There are elliptic scales, each with their own polar gnomon, on the four compass points.
In between, three-sided prisms make additional scales, the edges of the elliptical scales and the prisms serving for polar styles.

All these extra scales serve to increase the usefulness of this armillary sphere. Indeed, a single closed equatorial band would not allow any time readout around the equinoxes.

Notice the inscription on a number of rings in the armillary.
The proper designations are the subject of Article of the Month van april 2003.