History of the Telescope

In this article:

• Corrective lenses
• Invention of the telescope
• Galileo Galilei
• Timeline

What our ancestors didn’t know about the heavens could fill a book—and did, many times over, with fanciful notions about gods and other literally celestial beings, complex schemes of spheres to contain the stars, and, most crucially wrong, the idea that the sun revolves around the earth. That all began to change 400 years ago with the invention of the telescope.

But the telescope had ramifications beyond an improved understanding of astronomy. As the Rice University’s Galileo Project Web site puts it, “The telescope was one of the central instruments of what has been called the Scientific Revolution of the 17th century. It was the first extension of one of man’s senses, and demonstrated that ordinary observers could see things that the great Aristotle had not dreamed of. It therefore helped shift authority in the observation of nature from men to instruments. In short, it was the prototype of modern scientific instruments.”

In particular, of course, the telescope began to shift the balance of the debate between the geocentric view and Copernicus’ heliocentric theory. By moving earth-and humankind-from the center to merely another planet orbiting the sun, the telescope began a long process of taking humanity down a peg or two, which would continue with Charles Darwin.

Development of lenses
Despite its pivotal role in the Scientific Revolution, the telescope wasn’t invented by scientists. As the Galileo Project points out, “Rather, it was the product of craftsmen. For that reason, much of its origin is inaccessible to us since craftsmen were by and large illiterate and therefore historically often invisible.”

Nor was the telescope invented by Galileo Galilei (1564-1642), despite the invention’s popular association with the great Italian scientist. At least three Dutch craftsmen have claims to assembling the first telescope in 1608, a year before Galileo put one to use discovering the moon’s craters and four moons of Jupiter.

But these inventors were simply building on glassmaking technology that dates to at least the 13th century. That’s when magnifying glasses were first used to compensate for aging eyes’ declining ability to focus close up. Since holding a magnifying glass occupied one hand-cumbersome when writing-Venetian glassmakers tried using the nose instead. They created small glass disks that could be worn in pairs in a frame; the disks came to be called lenses, from the Latin for “lentils of glass.” The earliest illustrations of spectacles date from about 1350.

Birth of the telescope
Not for some 250 years would the idea of combining two opposite types of lenses to see distant objects occur, almost simultaneously, to Dutch spectacle makers. A convex (or converging) lens, thicker in the center than at the edges, causes light rays to refract inward to a single focal point, thereby correcting farsightedness. About 1450, glassmakers realized that by making a lens thicker at the edges than at the center, light could be refracted outwards; this concave (or diverging) lens could fix nearsightedness. Combine a convex and concave lens in a tube and you had a gadget “by means of which all things at a very great distance can be seen as if they were nearby.”

That earliest written description of a telescope, dated Sept. 25, 1608, is found on a letter from the provincial government of Zeeland, in the Netherlands, directing the Dutch States General to assist a spectacle maker named Hans Lipperhey. Born in Germany, Lipperhey had settled in Middelburg, the capital of Zeeland, and become a Dutch citizen in 1602. The States General debated Lipperhey’s patent application Oct. 2, 1608. The legislators couldn’t quite understand why his telescope design used only one eye, and asked Lipperhey to craft a double version-making him also the inventor of binoculars.

Although Lipperhey was handsomely rewarded, his patent application was ultimately denied because the design was too simple and couldn’t be kept secret. Indeed, soon after, another Dutch craftsman, Jacob Metius of Alkmaar, petitioned the States General, claiming to be the telescope’s inventor. A third inventor, Sacharius Janssen, also a Middleburg spectacle maker, apparently developed a telescope about the same time but missed the patent battle because he was busy trying to sell it at a fair in Frankfurt.

Focus on Galileo
Simple to construct, telescopes caught on quickly, and by April 1609 were for sale at shops on the Pont Neuf in Paris. That summer, Galileo crafted his own telescope, capable of magnifying distant objects three times. He first focused a 20-power telescope on the heavens in the fall of 1609, publishing his findings in Siderus Nuncius in March 1610.

But Galileo soon came to the attention of the Inquisition, which would ultimately place him under house arrest for the rest of his life. By the time of his death in 1642, ironically, Galileo was completely blind and unable to peer through his telescopes. They had shown him irrefutably, however, that the earth moves around the sun and not the other way around. “Eppur si muove!” Galileo legendarily muttered when forced to recant by the Inquisition in 1633—”and yet it moves!”

Astronomical Advancements
ca. 3500 BC Phoenicians, cooking on sand, discover glassmaking
424 BC Aristophanes uses a lens (a glass sphere filled with water) to start fires
circa 1350 Convex lenses are invented
circa 1450 Concave lenses are invented
1608 First written description of the refracting telescope credits Hans Lipperhey
1609 Galileo begins observations
1611 Prince Frederick Sesi, at a demonstration by Galileo, coins the term telescope; Johannes Kepler describes a telescope using two convex lenses, which results in a larger field of view but an upside-down image
1668 Isaac Newton builds the first reflecting telescope, using a mirror to dramatically increase the magnifying power
1673 Johannes Hevelius builds a 140-foot-long refracting telescope
1781 William Herschel discovers Uranus
1843 Ex-President John Quincy Adams dedicates Cincinnati observatory, the “birthplace of American astronomy”
1846 Johann Galle first observes Neptune
1897 Yerkes Observatory, the “birthplace of modern astrophysics,” opens
1930 Clyde Tombaugh discovers Pluto
1990 NASA launches the Hubble Space Telescope