Structure
An astrolabe is made up of 4 main pieces:
– the mater or base plate,
– the rete or top web-like plate which shows the fixed stars, the ecliptic (the zodiac constellations and part of the sky across which the Sun travels) and certain naked eye stars,
– the plates, each of which is made for a different latitude. Each plate has engraved on it a grid marking the zenith (point directly over head), the horizon and all the altitudes in between;
– the alidade or rule with sights used for making observations and reading off scales.
The rete and plates are designed to fit into the mater.