Important Astronomers, their Instruments and Discoveries

by Paul M. Rybski

Part 2

The Story of the Earliest, Nonachromatic Refracting Telescopes

Toward the Refracting Telescope

Invention of glass occurred about 3500 BC; it was first seen in Egypt. Working glass dates to 2000 BC when Phoenicians produced it in quantity. Earliest Greek references to optical properties: Aristophanes' "The Clouds" in 424 BC; Euclid on water flasks (250 BC?); Archimedes on military use of mirrors (XXX BC?).

Arabic astronomer al Hazen (950-1025 ?) explained atmospheric refraction on shapes of Sun and Moon close to the horizon. Italian astronomer Vitello (1230-1275) explained twinkling in stars and tried to establish laws of refraction.

Roger Bacon (1210-1294), a Franciscan monk working in Oxford, England, studied reflection and refraction in mirrors and lenses, respectively, suggesting lenses be used as magnifiers for close work. He also suggested the use of single lenses for viewing distant objects. He was imprisoned in his cell from 1281-1291 when results of his optical studies were condemned as witchcraft.

Italian monk Alexandro della Spina or Salvino d'Armati invented spectacles between 1285 and 1300.

English scholars Robert Recorde (1551) and Leonard Digges (1571) refer to use of "perspective glasses" to view distant objects, while Digges discusses mirrors being used similarly. William Bourne (1585) and Giambattista Della Porta (1589) claimed to have discovered a way to use two lenses to view distant objects, but neither manufactured a telescope.

Controversy over the Invention of the Refracting Telescope

Dutch spectacle maker Hans Lippershay filed a patent application in Holland on October 2, 1608, requesting exclusive rights to make and distribute "an instrument for seeing at a distance", consisting of a weak positive objective lens and a strong negative eyepiece. Lippershay constructed a telescope on request and was tested successfully; he received an initial contract for construction of up to three instruments.

Dutch spectacle maker Jacob Adriaanzoon filed a counterpetition, claiming he had constructed a telescope of power equal to Lippershay's and would construct one if he were paid to do it. Given the success in dealing with Lippershay, the Dutch authorities declined to pay for the construction.

Dutch spectacle maker Zacharias Jansen claimed to have invented the telescope prior to Lippershay and that the latter should not be granted an exclusive manufacturing patent. Despite a lack of evidence for prior invention from Adriaanzoon and Jansen, the Dutch government decided the issue too confused and refused to grant Lippershay's application.

Earliest uses of the Refracting Telescope

Italian mathematician and physicist Galileo Galilei (1564-1642) built his own telescopes in 1609 and 1610, revolutionizing astronomical observation: in January - March , 1610, he discovered the satellites of Jupiter and that the Milky Way consisted of faint stars too close together on the sky for the eye to see separately; in July, 1610, he discovered but could not explain the rings of Saturn; from October - December, 1610, he discovered the changing shape of Venus, concluding that Mercury and Venus shine by light reflected from the Sun about which they revolve; in July, 1611, he discovered sunspots and solar rotation.

German mathematician Johannes Kepler (1571-1630) studied and suggested improvements to the Galilean telescope (1611). From this study and from one of the eye, he suggested the use of a positive lens as an eyepiece. He also showed that spherically shaped lenses produce imperfect images due to their shape, a problem which can be eliminated by giving lenses hyperboloidal shapes instead of spherical ones.

Others built their own telescopes, corroborated Galileo's discoveries and extended them: Simon Marius discovered satellites of Jupiter (1609); Johannes Fabricius discovered sunspots (1611); Thomas Harriot determined the rotation period of the Sun (1611-1612); Fr. Christopher Scheiner developed an equatorially mounted telescope for solar observations (1612); Simon Marius discovered the galaxy M31 (1612); Johann Cysat discovered the Orion Nebula (1618); René Descartes studied plano-convex lenses (1637) using Willibrord Snell's (1621) law of refraction, showing that spherically shaped lenses can never provide a point focus for an object at infinity but that one with a hyperboloidal surface can; Giovanni Riccioli discovered satellite shadows on Jupiter and that Mizar in Ursa Major was a double star (1643); Anton Schyrle developed the terrestrial, or "image-erecting", eyepiece (1645) consisting of three lenses; several of these scientists suffered from the problem of late publication of discoveries.

Long-focus Refracting Telescopes

Observers discovered early on that they could minimize spherical and chromatic aberration by using telescopes of large focal ratio, i.e., small objective lenses with long focal lengths.

Dutch physicist Christian Huygens (1629-1695) and his brother Constantine found telescopes then obtainable too short, constructing first a 12 foot telescopes of 2 inch aperture, then one of 23 foot focus and, finally, one of 123 foot focus, from 1655-1659, during which they were observing Saturn and other objects. Their longest telescopes were constructed with the objective lens and eyepiece coupled only by a cloth cord. The objective lens was attached to a moveable platform attached to a tall pole and the eyepiece was mounted on a stand carried and pointed by the observer. While easily maneuvered, these telescopes could not be used except in total darkness. Christian Huygens reduced significantly the chromatic aberration of the objective lens. He also introduced the use of optical stops that reduced light reflected by the telescope tube walls and unwanted light from outer, less well shaped portions of the objective lens.

On March 25, 1655, Huygens discovered Saturn's largest moon Titan; in 1656, he independently discovered the Orion Nebula; in 1659, he published his analysis of Saturn's telescopic appearance in Systema Saturnium, announcing the discovery of its rings

Johannes Hevelius (1613-1686?) of Danzig, Germany, a brewer by profession, established his reputation as an astronomer by publishing his lunar atlas Selenographia in 1647, made with telescopes of less than 12 foot focal length and 50 magnification. Reading Christian Huygens' "Systema Saturnium", based on observations made with telescopes up to 123 feet in length, convinced Hevelius to construct much longer focal length telescopes that were 60, 70 and 150 feet in length. Constructed of square wooden frames and maneuvered by several assistants using pulleys attached to towers, these were difficult to point and keep aligned in conditions of changing temperature, humidity and wind speed.

Giovanni Cassini (1625-1712), while a professor of astronomy at Bologna, Italy from 1650-1671, made many planetary observations using telescopes built by the Italians Eustachio Divini of Bologna and Giuseppe Campini of Rome. By 1666, he had determined that Mars rotated in 24 hours 40 minutes; that Venus appeared to rotate in 23 hours 15 minutes; and that Jupiter revolved on its axis, was flattened with a polar or equatorial radius of 14/15 and had shadows of its satellites appear to cross its surface. On a visit to Paris in 1669, he improved the estimate of the Sun's rotation period with a Campini 17-foot telescope. In 1671 he moved to Paris to supervise the Paris Observatory, discovering a new satellite of Saturn. In 1672, using a 34 foot Campini telescope of five inch aperture, he discovered another of Saturn's satellites; using this same telescope in 1675, he discovered the division in the rings of Saturn that is now named after him. His last two discoveries of Saturn satellites occurred in 1684 using Campini telescopes of 100 and 132 foot focus.

English astronomer John Flamsteed (1647-1719) began his career as an enthusiastic amateur before becoming Astronomer Royal at Greenwich in 1675; the Greenwich charter was to assist navigation by providing correct star positions and reliable tables predicting the positions of the Sun, Moon and planets on a yearly basis; compared to other observatories at that time, Greenwich was poorly equipped, largely equipped at Flamsteed's personal expense and that of his friend Sir Jonas Moore. With the equipment available, apart from the needed tables for navigation, Flamsteed produced the star atlas "Historia Coelestis" whose accuracy was not challenged for more than a century following its printing.

Part 1       Part 3

PSC Home
Bill Arnett); last updated: 1997 Jan 12