# Aristarchos' and Archimedes' Cosmos

Comparison of Aristarchos' and Archimedes'

*Cosmos*.This reconstruction is based on Archimedes' descriptions:
According to Archimedes (

*Sandreckoner*1.4), ‘*cosmos*is the name given by most astronomers to the sphere whose centre is the centre of the earth and whose radius is equal to the straight line between the centre of the sun and the centre of the earth.’ He (*Sandreckoner*1.6) added that Aristarchos ‘appears to suppose the magnitude of the sphere in which he represents the earth as moving to be equal to what we [3c BC Greek astronomers] call the*cosmos*.’ Archimedes (*Sandreckoner*4.17) also said that ‘the ratio of the earth to what we commonly call the*cosmos*is equal to the ratio of this*cosmos*to the sphere of fixed stars, as proposed by Aristarchos: the two spheres have the same ratio to each other.’ Moving the ‘Sphere of Fixed Stars’ slider shows how a nearby target star shifts its position against the background of far away stars as seen from opposite ends of the earth's orbit.