Final answer:
To prove that the Earth is a sphere to a Flat Earth Society member, we can use historical and scientific evidence, such as the ancient Greeks' understanding of Earth's shape, the visible phenomena supporting a spherical Earth, and the consistent scientific consensus since the Scientific Revolution.
Step-by-step explanation:
When attempting to prove to a member of the Flat Earth Society that Earth is a sphere, we can reference various pieces of evidence that confirm our planet's spherical shape. Over 2000 years ago, educated individuals in the eastern Mediterranean region already knew Earth was round, with beliefs dating back to Pythagoras who regarded circles and spheres as 'perfect forms.' Sailors and scientists of ancient times not only suspected a spherical Earth but also estimated its size.
Contrary to the belief of some that Earth is flat, there's an overwhelming amount of evidence supporting its shape as an oblate spheroid. One fundamental reality is that Earth can only have one shape, which is evidenced by many different ways, including the phenomenon of ships disappearing hull-first over the horizon, the circular shadow cast on the moon during a lunar eclipse, and the variation of star constellations when traveling across the globe. The Scientific Revolution further solidified our understanding of Earth's shape and orbit, which continues to be accepted by the scientific community today.