Which letter do you think we use in place of the "f" on the above page?
A tool used to teach children about the universe, see the Earth in the middle?
An Astronomical clock
All the stars stuck to an invisible bubble surrounding the flat Earth? Sound legit to you?
The Earth at the centre of the universe? Of course! (At least their Earth is round and not flat)
Much of what we know came from the Islamic Arab World.
Link to the site: http://www.hps.cam.ac.uk/whipple/explore/astronomy/