What is straight?
How do you measure distance on a sphere?
How do you walk straight?
What are the ways to get/go straight?
What does when you flatten a string around a sphere you end up back at the start? Why does this give you a great circle?
What are lines in a sphere?
How many pts. do you need to get a great circle?
How many pts do you need for a sphere?
Is there always a unique great circle through 2 pts?
What is the definition of on opposite pt to a given pt?
What are the only circles that if you take the opposite pts you get pts on the same circle?
How is parallel defined on a sphere?
Why are only great circles straight?
How do you measure distance on the surface of a sphere?
How can a circle on a sphere have two centers?
What is the antipodal pt of