When we were walking lonely avenue.

When you look at the sky, you see what looks like stars stuck on the inside of a great sphere centered on the Earth. Because the distances are so large, they appear to be the same. This makes it look like the Earth is on the center of a great sky abbyss. All the stars seem to be infinitely far away. We can't fault the ancients for seeing the sky as a hollow circle; it certainly looks that way. Most of the time, staring.