One of Galileo’s first recorded telescopic observations was of Jupiter and “three fixed stars, totally invisible by their smallness”—three of the four large moons of Jupiter. Wne now call the four large moons of Jupiter the Galilean Satellites or moons. In 1668, Sir Isaac Newton designed and built the first Reflecting Telescope. It was Galileo who first described the idea for a reflecting-type telescope. The Reflecting Telescope used a concave mirror in the place of a lens to focus incoming light.
Public Domain | Image courtesy of NASA.
