because you've been told, that the Earth revolves around the Sun. You also probably know that planets other than our own have moons, and the way to test to see whether or not something is true is by experimenting. Thousands of years ago, these things were not widely known. The heavens above were anyone's guess, and the way things were was just the way the gods had made them. It was felt there was no need to truly understand them or put them in any kind of order.
The Greek scholars changed much of that. They were famous for their schools of higher knowledge, which were rather different than ours. Students would gather around a teacher, perhaps in a beautiful grove, and ask questions and discuss among themselves what might be the answers and the best ways to figure out those answers. Many of today's colleges still aspire to this way of learning.
