Galileo Demonstrates the Telescope . ... Upon hearing at age 40 that a Dutch optician had invented a glass that made distant objects appear larger, Galileo crafted his own telescope and turned it toward the sky . Galileo quickly discovered that our Moon had craters , that Jupiter had it's own moons , that the Sun has spots , and that Venus has phases like our Moon. Galileo , who lived from 1564 to 1642, made many more discoveries. ... NASA Web Site Statements, Warnings, and Disclaimers . ...