Astrolabe

The astrolabe is an ancient astronomical calculator for determining time and the positions of the Sun and stars.

There are several types of astrolabe including the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator.

Astrolabes were typicaly made from brass with a diameter of around 15cm.

http://www.astrolabes.org/fusweblg.gif An astrolabe