Has anyone ever seen with their own eyes that the Earth goes around the sun? Even to this day, no one has. However, 500 and even 2000 years ago, some astronomers managed to point out that this is the case. At that time, people’s range of activities was strictly confined, the technology and tools used were extremely primitive, and many of the mathematical methods used today had not been developed. How did those astronomers make and verify this discovery? This book explains this exciting demonstration process. It enables anyone with a basic junior-high-school knowledge of geometry and a certain degree of spatial imagination to understand this and other interesting discoveries in the solar system. By demonstrating this interesting process, the book not only satisfies readers' curiosity using the simplest mathematics, but also inspires them to explore the new and unknown world.