Who Invented the Telescope?
Hans Lipperhey, Jacob Metius, and Zacharias Janssen in the Netherlands around 1608: the contested invention of the refracting telescope and its rapid spread across Europe.
Who Invented the Telescope?
The refracting telescope — the first instrument to extend human vision to the heavens — was invented in the Netherlands in 1608. The invention was contested at the time and has remained contested among historians. Three names are most often associated with it: Hans Lipperhey, a spectacle-maker of Middelburg; Jacob Metius, also of Middelburg; and Zacharias Janssen, whose instrument-making shop in the same town is documented, although the surviving evidence is ambiguous.
This page is an article in the Telescope and Microscope, under the Major Discoveries. It assumes familiarity with the broad context, which is sketched in the section overview. For Galileo’s improvements and telescopic discoveries, see Galileo’s Telescope Discoveries and the Galileo. For Newton’s reflecting telescope, see Newton and Optics.
The Patent Application of 1608
The most concrete piece of evidence for the invention of the telescope is the patent application that Hans Lipperhey (sometimes Lippershey) submitted to the States General of the Netherlands on 25 September 1608. Lipperhey, a German-born spectacle-maker established in Middelburg, requested a patent for “a certain device by which one can see far away things as though they were nearby.” The device, he explained, consisted of a tube containing a convex and a concave lens, by means of which distant objects appeared larger and clearer.
The States General did not grant the patent — partly because the device was already considered easy to imitate — but it did reward Lipperhey with a commission to build three binocular versions for military use, and it ordered the details of the instrument to be kept secret. The secret did not last long. Within months, reports of the new device were circulating across Europe, and copies were being made in spectacle-making shops in Italy, France, and England.
Jacob Metius
Within a few days of Lipperhey’s application, another Middelburg spectacle-maker, Jacob Metius (the brother of the mathematician Adriaan Metius), submitted a competing claim. The States General tested both devices and awarded a smaller reward to Metius. Whether Metius had independently arrived at the same design or had heard of Lipperhey’s work is not clear. The two applications together are the strongest evidence that the telescope was invented in Middelburg in 1608, by spectacle-makers who were working with the same kinds of lenses they used in eyeglasses.
Zacharias Janssen
The third claimant, Zacharias Janssen, is the most controversial. A late seventeenth-century memoir by Zacharias’s son, Johannes Zachariassen, claimed that his father had invented the compound microscope in 1590 and the telescope in 1604. Modern historians treat this memoir with caution: it is the only source for the early date, and the memoir’s details (including the claim that the elder Janssen had shown a compound microscope to the Archduke Albert in 1590) are not independently corroborated. Some historians accept that Janssen was involved in the early production of compound microscopes, but most date the telescope to 1608 and the work of Lipperhey and Metius.
What is clear is that spectacle-makers in Middelburg had the technical skills to combine a convex and a concave lens in a tube, that several of them did so in 1608, and that the device spread across Europe within a year. The dispute over priority is a reminder that important inventions are often the work of many hands, and that the documentation of an invention is a historical problem in its own right.
How the Telescope Works
A refracting telescope, in its simplest form, is a tube containing two lenses. The objective lens, at the front, has a long focal length. The eyepiece lens, at the back, has a short focal length. The objective gathers light from a distant object and forms a real image inside the tube, near the eyepiece. The eyepiece then acts as a simple magnifier, producing a large virtual image for the observer’s eye.
In Lipperhey’s and Galileo’s design, the eyepiece is a diverging (concave) lens, and the image is upright. This is called a Galileian telescope. It has the disadvantage of a small field of view, but it is short, compact, and produces an erect image, which is why it is the configuration still used in opera glasses today.
In 1611, Johannes Kepler proposed a design with a converging eyepiece, producing an inverted but sharper image with a wider field of view. The Keplerian telescope is the basis of all modern astronomical refractors. The inversion does not matter for astronomical observation, since there is no “up” in space.
The magnification of a simple refracting telescope is approximately the ratio of the focal length of the objective to the focal length of the eyepiece. Lipperhey’s first telescope had a magnification of about three diameters. Galileo’s best telescopes, made in 1610, had magnifications of about twenty to thirty diameters.
The Rapid Spread to Italy
The first telescope to reach Italy was built in late 1608, almost certainly by a spectacle-maker in Venice or Padua. By April 1609, several telescopes were available in Venice, and the Venetian senate gave the Paduan senator and scientist Paolo Sarpi the task of investigating the new device. Sarpi corresponded with Galileo, who was at the University of Padua, and news of the invention reached Galileo in June 1609.
Galileo, who was already familiar with the optics of lenses, immediately set to work building his own telescopes. He developed methods for grinding and polishing lenses that produced sharper images than the Dutch originals, and within a few months he had constructed instruments of twenty diameters magnification. In August 1609, he demonstrated one of his telescopes to the Venetian senate, who appreciated its military value in spotting ships at a distance. By December 1609, he had improved his instruments to about thirty diameters and was ready to turn them on the night sky.
Sidereus Nuncius
In March 1610, Galileo published his telescopic observations under the title Sidereus Nuncius (The Starry Messenger). The book contained four major discoveries, each announced with care and supported by careful drawings and sequences of nightly observations:
- The Moon’s surface was not a perfect sphere: it had mountains, valleys, and craters, and the terminator (the line dividing the lit and unlit halves) showed a jagged profile consistent with a rough surface.
- The Milky Way was not a continuous luminous cloud but a dense mass of individual stars too faint to be seen with the naked eye.
- Jupiter had four “Medicean stars” — now called the Galilean moons — that changed position from night to night in a way that made sense only if they were orbiting Jupiter.
- Hundreds of new stars, too faint for the naked eye, were visible in familiar constellations and in the nebulae.
Each of these discoveries is described in detail in Galileo’s Telescope Discoveries. Their cumulative effect on cosmology is treated in the Heliocentrism and the New Astronomy section.
Newton’s Reflecting Telescope
The refracting telescope of Galileo’s day had two principal limitations. The first was chromatic aberration: a single lens focuses different colours of light at slightly different distances, producing a coloured halo around bright objects. The second was the difficulty of making large, flawless lenses: a small piece of bad glass or a poorly figured surface would degrade the image.
Isaac Newton analysed the problem in the early 1670s and concluded that chromatic aberration was inherent in any refracting telescope. He proposed to replace the objective lens with a curved mirror, which reflects all colours equally and so does not suffer from chromatic aberration. He built his first reflecting telescope in 1668 — a small instrument with a mirror about three centimetres in diameter, mounted at the bottom of a tube, with a small flat mirror tilted at forty-five degrees to send the image to an eyepiece set in the side of the tube. The instrument performed as well as a refractor several times its length, and it is the prototype of all modern Newtonian reflectors.
Newton’s design, and the optical theory behind it, is described in Newton and Optics. The reflecting telescope proved crucial for the growth of large astronomical instruments in the eighteenth and nineteenth centuries, culminating eventually in space-based observatories such as the Hubble Space Telescope and the James Webb Space Telescope.