Skip to content
One Long Tail
Lessons
Hands-on
Plans
About us
Menu
Lessons
all 428, by branch
Hands-on
lessons you can touch
Plans
what we're building
About us
who we are, contact
All physics lessons
Physics
Lesson 7 of 104
Ptolemy and looping orbits
Why do the planets go backwards?
600 BC
today
Era 1 of 10:
Sky and Earth
, 600 BC – AD 1350
Check yourself
Loading exercises…