There are a number of conflicting claims for the first person to combine two lenses to “see things far away as if they were nearby.” The Dutch eyeglass makers Hans Lippershey, Sacharias Jansen, and Jacob Metius were some of the first. Lippershey described the design and applied for a patent on October 8, 1608, but was turned down. Copies of Lippershey’s device, which was constructed from a convex and a concave lens and had a magnifying power of 3, were common in the Netherlands that year. Galileo (1564-1642) heard about the invention in June 1609, in Venice. By the next day he had figured out how it worked and as soon as he returned home to Padua he constructed one. A few days later he demonstrated it to the leaders in Venice, who, in return awarded him a lifetime position at the University in Padua. Over the next year Galileo improved his instruments, and in 1610, using a telescope with a magnifying power of 33, he discovered the moons of Jupiter, the rotation of the sun, phases of Venus, spots on the sun, and mountains on the moon. The Galilean telescope with convex and concave lenses produces an upright image.

Based on the ideas of astronomers Johannes Kepler (1571-1630) and Christoph Scheiner, the telescope was improved by using two convex lenses separated by a distance equal to the sum of their focal lengths. Such a telescope inverts the image. To achieve high magnifications one of the focal lengths had to be very large. Refracting telescopes proved to be cumbersome and difficult to use. The prism-like shape of the lenses introduced colors into the images that weren’t there. This defect, called chromatic aberration, was eliminated 120 years later using a lens made of a combination of two glasses. But this invention did not stop the weight of the large lens from causing it to sag, creating distorted images.

Reflecting telescopes that use mirrors to focus light, were invented by Isaac Newton (1642-1727) in 1668. Today, telescopes, both refractors and reflectors, are relatively cheap; the average person can set one up in his or her backyard and gaze up at the heavens with much better equipment than Galileo or Newton ever dreamed possible.