Some lights will not stay still.

A working reconstruction of a mid-latitude night. Most of the lights keep their pattern from night to night. Those are the fixed stars. A few bright lights shift against that background over days and months. Those wanderers became the planets visible to the naked eye.

Before telescopes, that was already a problem: if the sky is a reliable order, why will some of it not stay still? PLANETAI follows what happened when people tried to answer.