The telescope is an optical instrument made with lenses and mirrors which shows magnified views of distant objects. The invention of the refracting telescope (or "spyglass") is usually credited to Hans Lippershey. When Galileo Galilei encountered the spyglass, he made himself a much more powerful one, and was the first person in history to make detailed recorded observations of the objects in the nighttime sky.
Galileo discovered lights that went back and forth around the planet Jupiter, which we now know as the four largest moons of Jupiter. These can seen by anyone with a pair of modern binoculars; they usually look like three or four stars that are close to Jupiter and all lined up in a straight line. This discovery was important because at the time philosophers and theologians believed that everything in the universe revolved around the Earth. They believed that the geocentric design reflected the will of God.
The simplest telescopes (e.g., the kind Galileo worked with) are built with two lenses in a tube (see Refraction).
- Most of the history of astronomical telescopes has been dominated by either Keplerian refractors or Cassegrainian reflectors. The Cassegrain telescope was proposed by a priest. The Keplerian telescope was first proposed by Johannes Kepler, but first built by the Catholic priest, Christopher Scheiner. 
During the twentieth century, astronomers built huge telescopes. Some of the most famous in the United States are: