A mass of innumerable stars

The telescope, from the uncertain patent to Galileo's and Kepler's discoveries

By Museo Galileo - Istituto e Museo di Storia della Scienza

Galileo's objective lens (1609/1610)Museo Galileo - Istituto e Museo di Storia della Scienza

The
invention

The question of who was the first to invent the telescope is as old as the instrument itself. On October 2, 1608, the Dutch Estates General examined an application for a patent for "a device to observe things at a distance" presented by a certain Hans Lipperhey (?-1619), an obscure spectacles-maker from Middelburg, in southwestern Holland. The patent application was rejected on the grounds that, although the usefulness of the device was recognised, especially for military purposes, it was deemed impossible to keep the secret of its construction for very long. 

La dioptrique oculaire... (1670) by Chérubin d'Orléans, pèreMuseo Galileo - Istituto e Museo di Storia della Scienza

And especially considering that, in those same days, another instrument-maker, Sacharias Janssen (1588-1630), he too a spectacles-maker in Middelburg, indicated by Pierre Borel (c. 1620-1671) a few decades later as the true inventor of the telescope – declared that he knew how to build the instrument.

Galileo's telescopeMuseo Galileo - Istituto e Museo di Storia della Scienza

News of the invention spread rapidly throughout Europe, and already by April 1609 little telescopes about thirty centimetres long were to be found on sale, at the shops of spectacle-makers, in Paris and presumably in London.

In Italy, the new instrument made its appearance at Milan in May of the same year, and two or three months later in Rome, Naples, Padua and Venice, where Fra Paolo Sarpi (1552-1623), a friend of Galileo, had heard news of it already by November 1608.

Galileo Galilei offre al Senato Veneto il suo cannocchiale by Ulacacci, Nicola sec. XIXMuseo Galileo - Istituto e Museo di Storia della Scienza

From the
workshop to the stars

Galileo (1564-1642) fabricated his first telescope, with only three magnifications, in the summer of 1609. But already on August 21 of that year, in the bell tower of San Marco, in the presence of the Doge and other Venetian notables, he presented an instrument that had eight magnifications, and that won him a lifetime appointment to the Padua Chair of Mathematics at a salary of one thousand florins a year.

Portrait of Galileo Galilei (1613) by Francesco Villamena|Galileo GalileiThe Metropolitan Museum of Art

In November, Galileo had at his disposal a telescope with twenty magnifications, that is, more powerful by far that all the others circulating through Europe at the time, which utilised ordinary lenses made for spectacles, of low quality and with unsuitable focal lengths.

Lettera di Galileo Galilei a Belisario Vinta nella quale annuncia la natura tricorporea di Saturno by Galilei, Galileo 1564-1642Museo Galileo - Istituto e Museo di Storia della Scienza

Carta manoscritta con disegni della Luna by Galileo GalileiMuseo Galileo - Istituto e Museo di Storia della Scienza

The instruments developed by Galileo were highly superior in performance, for example, to the telescope with six magnifications with which the Englishman Thomas Harriot (1560-1621) had conducted observations and made drawings of the lunar surface in July 1609.

Bust of Galileo and its tools in the Museo Galileo in FlorenceMuseo Galileo - Istituto e Museo di Storia della Scienza

Thanks to the power of his instrument, Galileo achieved exceptional results in his observations of the moon, demonstrating, in fact, that its surface is not perfectly spherical nor immaculate and even managing to calculate the height of the lunar mountains.

Frontespizio del Sidereus nuncius by Galilei, Galileo 1564-1642Museo Galileo - Istituto e Museo di Storia della Scienza

Subsequently, Galileo was to make the exceptional series of astronomical discoveries, described in the Sidereus Nuncius [The Starry Messenger] published in March 1610, and destined to revolutionize forever the traditional view of the cosmos.

Seconda parte del disegno raffigurante la costellazione delle Pleiadi, come vista da Galileo con il telescopio by Galilei, Galileo 1564-1642Museo Galileo - Istituto e Museo di Storia della Scienza

He was to discover, first of all, the existence of a myriad of new stars, showing that the Milky Way is "no other than a mass of innumerable stars scattered in clusters".

Saturno, Giove, Marte e Venere con le proprie fasi by Galilei, Galileo 1564-1642Museo Galileo - Istituto e Museo di Storia della Scienza

And again, he was to observe the strange appearance of Saturn, whose true cause, the presence of a ring around the planet, was to be found by Christiaan Huygens (1629-1695) nearly half a century later.

He was the first to observe the phases of Venus, which conclusively demonstrated that the planet moved, orbiting around the Sun.

Osservazioni di Giove e dei Pianeti Medicei by Galilei, Galileo 1564-1642Museo Galileo - Istituto e Museo di Storia della Scienza

But the discovery that brought him immortal fame, in January 1610, was that of the four satellites of Jupiter, which Galileo, in homage to the dynasty that ruled Tuscany, named Astri Medicei, or Medicean Planets.

Galileo showing the Medicean planets (Jupiter’s satellites) to the allegories of Optics, Astronomy and Mathematics (in: Galileo Galilei “Opere”. Bologna, 1656) (1656/1656) by Galileo GalileiMuseo Galileo - Istituto e Museo di Storia della Scienza

Diario delle osservazioni dei satelliti di Giove by Galileo GalileiMuseo Galileo - Istituto e Museo di Storia della Scienza

LIFE Photo Collection

The
Keplerian telescope

The Galileian telescope furnishes erect images, but has an extremely narrow field of view, which rapidly diminishes with increasing magnification. If, in fact, the field of view of a Galileian telescope with twenty magnifications is indicatively 15 minutes, that is, about half the apparent diameter of the Moon, it decreases to the order of only 5 minutes in a telescope with fifty magnifications. Such limited fields not only made the Galilean telescope unfeasible for civil and military purposes, but above all prevented, in the astronomical field, increments in performance over a few tenths of a magnification.

Osservazioni astronomiche: Giove e i Pianeti Medicei by Creti, Donato 1671-1749Museo Galileo - Istituto e Museo di Storia della Scienza

Johannes Kepler (1571-1630), the German astronomer famous for his three laws on planetary motion, had however demonstrated, since 1611, the possibility of replaced the diverging eyepiece of the Galileian telescope with a converging lens, with the ensuing advantage of a much vaster and more highly contrasted field of view.

But this optical combination, known today as the Keplerian (or astronomical) telescope, furnished upside-down images that made it unsuitable for terrestrial use.

Osservazioni astronomiche: Mercurio by Creti, Donato 1671-1749Museo Galileo - Istituto e Museo di Storia della Scienza

Galileo (1564-1642) was to remain always faithful to the optical combination that bears his name.

However, in the 1630s, the Keplerian telescope began to be widely used, mainly due to the work of the Neapolitan optician Francesco Fontana (c. 1580-1656), to the point of entirely superceding the Galileian one toward the middle of the century.

Osservazione della Luna by Donato CretiMuseo Galileo - Istituto e Museo di Storia della Scienza

The last great astronomical achievement made with a telescope of this type, published by Hevelius (1611-1687) in 1647, was the representation of the lunar surface.

Moreover, the Keplerian telescope soon predominated for terrestrial purposes as well, thanks to the introduction of the so-called erector, an optical device, usually consisting of two convex lenses with the same focal length, which turned the image produced by the objective upright.

Credits: Story

Curator: Sara Bonechi

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