For several thousand years, humanity has looked at the sky and informed itself about the workings of the universe. Many early cultures refrained from developing technologies to examine the cosmos because of their belief in the existence of an omnipotent and unpredictable god who controlled existence. However, some ancient cultures have evidence of their first astronomical discoveries. For example, the Chinese have records dating back to 1300 BC. Around 750 BC, the Babylonians discovered the 18.6-year cycle in the rising and setting of the moon and compiled almanacs to predict eclipses. Around 600 BC, the Greeks began to develop an interest in astronomy. The Greeks were the main source of authority on astronomy. The ideas and discoveries of the Greek philosophers spread and were widely accepted. The Greeks were the first to discover that the Earth was spherical, and one particular Greek astronomer named Eratosthenes even measured the circumference of the Earth and the tilt of the Earth's axis with incredible precision. Around 150 AD, an astronomer named Ptolemy invented the...