Hemisferium Hanging Altitude Ring dial (40º or 50º Lat.)

15th-century mariners found a way to estimate their latitude to find their location while at sea. It was based on a well-known fact that the height of celestial bodies depends on the latitude.

The Altitude sundial takes this name because the parameter of its construction is based on Sun’s altitude. This brass scientific instrument is available for two different latitudes: 40º or 50º.

The dial is composed of a circular band punched with two offsetting symmetrical holes through which the sun rays pass are projected as small, elongated spots of light on the hourly line etched on the interior of the dial. Pedro Nunes, a Portuguese mathematician, cosmologist and professor invented the nonius, a system for taking small measurements on circular instruments such as the ring dial and the astrolabe, allowing for more accurate positioning of ships.

The ring dial measures 40mm across, 21mm wide and 4mm thick and comes complete hanging on a chord.