Spyglass turned to the sky
Two spectacle lenses fitted at the ends of a tube. In the autumn of 1608 the Dutch spectacle maker Hans Lipperhey of Middelburg showed such an instrument in The Hague and asked for a patent, which was refused because other makers claimed the same.
In 1609 the Italian Galileo Galilei, having heard of the 'Dutch glass', ground lenses himself, raised the magnification to twenty and turned the tube on the sky. In the Sidereus nuncius (March 1610) he reported mountains on the Moon and the satellites of Jupiter, and in 1610 he saw the phases of Venus.
The question of the centre of the world becomes a matter of observation, not of philosophy.
Why this date
exact for the documents: letter of the States of Zeeland of 25 September 1608 and Lipperhey's petition to the States General of 2 October 1608; turned to the sky in 1609 (Harriot 26 July, Galileo from November-December); the inventor is unknown
What it grew from
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Ground lens and eyeglasses
prerequisite for · Confidence: high
The first telescopes were assembled from spectacle lenses by spectacle makers: Lipperhey was a Middelburg spectacle maker, and optical examination of the earliest surviving telescopes shows that all their lenses are of spectacle glass.
Dispute: The dependence itself is undisputed; the dispute is why it bore fruit only after 300 years. Willach: 14th to 16th century spectacle lenses from blown balls were astigmatic and served the eye (2 mm pupil) but not an objective; the telescope became possible when lenses were ground in concave moulds and a diaphragm was added to the tube. Zik and Hon (PhilArchive, undated) argue that Galileo improved the tube using Della Porta's theory of refraction, not by trial alone.
Link sources
- Willach R. «The Long Route to the Invention of the Telescope», Transactions of the American Philosophical Society 98(5) (2008) Verified 20 Sep 2026
Optical examinations of the earliest surviving telescopes clearly indicate that the lenses of all these instruments are of spectacle glass.
- Zuidervaart H. J. «The 'true inventor' of the telescope. A survey of 400 years of debate», in: The Origins of the Telescope, KNAW Press (2010), 12 Verified 25 Sep 2026
The archives of the States General in The Hague reveal that 'the bearer of this letter' was in fact the Middelburg spectacle maker Hans Lipperhey, born in Wesel ca. 1570
- Willach R. (2008) Verified 20 Sep 2026
The glassblowing technique, as ingenious as it was, was a dead end as far as the invention of the telescope is concerned.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Willach R. «The Long Route to the Invention of the Telescope», Transactions of the American Philosophical Society 98(5) (2008) Verified 20 Sep 2026
What grew out of it
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Mathematical Principles of Natural Philosophy
influenced · Confidence: high
The argument of Book III of the Principia opens with telescopic data: Phenomenon I (the satellites of Jupiter, measured with a micrometer in a telescope) extends the inverse-square law beyond the planets; Kepler's laws themselves, however, were derived from Tycho's pre-telescopic observations.
Dispute: For a strong dependence: the satellites of Jupiter (Phenomenon I) and Saturn (Phenomenon II) cannot be observed without a telescope, and it is with them that Newton begins the proof of the universality of gravitation. Against it: Kepler's three laws, the Moon test and the inverse-square law for the planets rest on Tycho Brahe's pre-telescopic data and on the ancient estimate of the Moon's distance; without the telescope the book would have appeared in a narrower form, but it would have appeared. The quote about the micrometer and the 123-foot telescope comes from the third edition (1726), where Pound's data replaced the Cassini and Flamsteed measurements of the first edition of 1687.
Link sources
- Newton I. Philosophiae Naturalis Principia Mathematica, 3-. 1726, III, I (1726)
The diameter of Jupiter was often taken from the micrometer in the 123 feet telescope, and reduced according to the mean distance of Jupiter from the sun or the earth, always produced an image less than 40'', at no time less than 38", more often 39".
- Britannica, «Isaac Newton: The Principia» (2024) Verified 24 Sep 2026
Because the satellites of Jupiter also obey Kepler's third law, an inverse square centripetal force must also attract them to the center of their orbits.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.
- Newton I. Philosophiae Naturalis Principia Mathematica, 3-. 1726, III, I (1726)
Node sources
- Zuidervaart H. J. «The 'true inventor' of the telescope. A survey of 400 years of debate», in: Van Helden A. et al. (eds.), The Origins of the Telescope, KNAW Press, pp. 9-44 (2010), 11-12 Verified 25 Sep 2026
The archives of the States General in The Hague reveal that 'the bearer of this letter' was in fact the Middelburg spectacle maker Hans Lipperhey, born in Wesel ca. 1570
- Zuidervaart H. J., p. 20 (2010), 20
As a matter of fact, in his Sidereus Nuncius, published in March 1610, Galilei admitted that the telescope had originated in the Netherlands
- Christie T. «The telescope: claims and counterclaims», The Renaissance Mathematicus (2018) Verified 20 Sep 2026
On 2 October 1608, Lipperhey submitted an application for a patent for his device to the States-General
- MacTutor History of Mathematics, «Galileo Galilei» Verified 20 Sep 2026
By the end of 1609 Galileo had turned his telescope on the night sky and began to make remarkable discoveries.
- Linda Hall Library, «Scientist of the Day: Thomas Harriot» Verified 20 Sep 2026, quotation assembled from fragments
On July 26, 1609, Harriot made a sketch of the moon, as viewed through his telescope ... This was the first documented drawing of any astronomical object seen through a telescope, anticipating Galileo's first watercolors of the moon by over four months.
"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong. "Assembled from fragments" means the words do not stand together on the page: we found each fragment separately and joined them with an ellipsis.
Further reading
Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.