From ancient times, humans looked at the moon and wondered what it was, and if it were possible to go there.
Prior to the invention of the telescope, people thought the moon was simply a glowing disc in the sky, and planets were moving points of light. Nothing else was known about them.
When 17th-century Italian astronomer Galileo first pointed a crude telescope at the moon, he noted that the orb had terrain including mountains, flat plains and craters. Therefore, the moon was solid, and its surface might be walked upon.
Source SPACE.com: All about our solar system, outer space and exploration.
