Astronomy Project Sources

Callippus:
1. http://www-history.mcs.st-andrews.ac.uk/Biographies/Callippus.html
2. http://astronomy.swin.edu.au/cosmos/C/Callippus

Eudoxus
1. http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Eudoxus_of_Cnidus.html
2. http://www.calstatela.edu/faculty/hmendel/Ancient%20Mathematics/Eudoxus/Astronomy/EudoxusHomocentricSpheres.htm