Sidereus Nuncius

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Sidereus Nuncius
Houghton IC6.G1333.610s - Sidereus nuncius.jpg
Title page of the first edition.
Author Galileo Galilei
Country Republic of Venice (now Italy)
Language New Latin
Subject Astronomy
Publisher Thomas Baglioni
Publication date
March 1610

Sidereus Nuncius (usually Sidereal Messenger, also Starry Messenger or Sidereal Message) is a short astronomical treatise (or pamphlet) published in New Latin by Galileo Galilei in March 1610. It was the first published scientific work based on observations made through a telescope, and it contains the results of Galileo's early observations of the imperfect and mountainous Moon, the hundreds of stars that were unable to be seen in either the Milky Way or certain constellations with the naked eye, and the Medicean Stars that appeared to be circling Jupiter.[1]

The Latin word nuncius was typically used during this time period to denote messenger; however, it was also (though less frequently) rendered as message. Though the title Sidereus Nuncius is usually translated into English as Sidereal Messenger, many of Galileo's early drafts of the book and later related writings indicate that the intended purpose of the book was "simply to report the news about recent developments in astronomy, not to pass himself off solemnly as an ambassador from heaven."[2] Therefore, the correct English translation of the title is Sidereal Message (or often, Starry Message).

A copy of the original edition is a valuable rare book and as of December 2010 has sold at auction for USD $662,500, including premium.[3]


Although it is unclear who built the first telescope, its invention is commonly credited to Hans Lippershey, a German-Dutch lensmaker. The telescope allows the user to view distant objects as if they were much closer and larger. Galileo was one of the first to use the telescope to view and describe celestial bodies.[4] One of Galileo’s first "Optical Canons," as he referred to them, had 8-10 enlargements (8x to 10x magnification) and was made out of lenses that he had ground himself.[5] This increased to the 20-enlargement telescope that he used to make the observations in Sidereus Nuncius.[6]


Galileo's sketches of the moon from Sidereus Nuncius.

Sidereus Nuncius contains more than seventy drawings and diagrams of the Moon, certain constellations such as Orion, Pleiades, and Taurus, and the Medicean Stars of Jupiter. Galileo's text also includes descriptions, explanations, and theories of his observations.


In observing the Moon, Galileo saw that the line separating lunar day from night (the terminator) was smooth where it crossed the darker regions of the moon but quite irregular where it crossed the brighter areas. From this he deduced that the darker regions are flat, low-lying areas, and the brighter regions rough and mountainous. Basing his estimate on the distance of sunlit mountaintops from the terminator, he judged, quite accurately, that the lunar mountains were at least four miles high. Galileo’s engravings of the lunar surface provided a new form of visual representation, besides shaping the field of selenography, the study of physical features on the Moon.[1]

Galileo's drawings of the Pleiades star cluster from Sidereus Nuncius. Image courtesy of the History of Science Collections, University of Oklahoma Libraries.


Galileo reported that he saw at least ten times more stars through the telescope than are visible to the naked eye, and he published star charts of the belt of Orion and the star cluster Pleiades showing some of the newly observed stars. With the naked eye observers could see only six stars in the Taurus constellation; through his telescope, however, Galileo was capable of seeing thirty-five – almost six times as many. When he turned his telescope on Orion, he was capable of seeing eighty stars, rather than the previously observed nine – almost nine times more. In Sidereus Nuncius, Galileo revised and reproduced these two star groups by distinguishing between the stars seen without the telescope and those seen with it.[7] Also, when he observed some of the "nebulous" stars in the Ptolemaic star catalogue, he saw that rather than being cloudy, they were made of many small stars. From this he deduced that the nebulae and the Milky Way were "congeries of innumerable stars grouped together in clusters" too small and distant to be resolved into individual stars by the naked eye.[6]

Galileo's drawings of Jupiter and its Medicean Stars from Sidereus Nuncius. Image courtesy of the History of Science Collections, University of Oklahoma Libraries.

Medicean Stars (Moons of Jupiter)[edit]

In the last part of Sidereus Nuncius, Galileo reported his discovery of four objects that appeared to form a straight line of stars near Jupiter. On the first night he detected a line of three little stars close to Jupiter parallel to the ecliptic; the following nights brought different arrangements and another star into his view, totalling four stars around Jupiter.[8] Throughout the text, Galileo gave illustrations of the relative positions of Jupiter and its apparent companion stars as they appeared nightly from late January through early March 1610. That they changed their positions relative to Jupiter from night to night and yet always appeared in the same straight line near it, persuaded Galileo that they were orbiting Jupiter. On January 11 after 4 nights of observation he wrote:

"I therefore concluded and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun; which at length was established as clear as daylight by numerous subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter...the revolutions are so swift that an observer may generally get differences of position every hour."[9]

In his drawings, Galileo used an open circle to represent Jupiter and asterisks to represent the four stars. He made this distinction to show that there was in fact a difference between these two types of celestial bodies. It is important to note that Galileo used the terms planet and star interchangeably, and “both words were correct usage within the prevailing Aristotelian terminology.”[10]

At the time of Sidereus Nuncius' publication, Galileo was a mathematician at the University of Padua and had recently received a lifetime contract for his work in building more powerful telescopes. He desired to return to Florence, and in hopes of gaining patronage there, he dedicated Sidereus Nuncius to his former pupil who later became the Grand Duke of Tuscany, Cosimo II de' Medici. In addition, he named his discovered four moons of Jupiter the "Medicean Stars," in honor of the four royal Medici brothers. This helped him receive the position of Chief Mathematician and Philosopher to the Medici at the University of Pisa.[6] Ultimately, his effort at naming the moons failed, for they are now referred to as the "Galilean moons."


The reactions to Sidereus Nuncius, ranging from appraisal and hostility to disbelief, soon spread throughout Italy and England. Many poems and texts were published expressing love for the new form of astronomical science. Three works of art were even created in response to Galileo’s book: Adam Elsheimer’s The Flight into Egypt (1610), Lodovico Cigoli’s Assumption of the Virgin (1612), and Andrea Sacchi’s Divine Wisdom (1631).[6] In addition, the discovery of the Medicean Stars fascinated other astronomers, and they wanted to view the moons for themselves. Their efforts “set the stage for the modern scientific requirement of experimental reproducibility by independent researchers. Verification versus falsifiability…saw their origins in the announcement of Sidereus Nuncius.[10]

But many individuals and communities were sceptical. A common response to the Medicean Stars was simply to say that the telescope had a lens defect and was producing illusory points of light and images; those saying this completely denied the existence of the moons.[10] That only a few could initially see and verify what Galileo had observed supported the supposition that the optical theory during this period “could not clearly demonstrate that the instrument was not deceiving the senses.”[11] By naming the four moons after the Medici brothers and convincing the Grand Duke Cosimo II of his discoveries, the defence of Galileo’s reports became a matter of State. Moran notes, “the court itself became actively involved in pursuing the confirmation of Galileo’s observations by paying Galileo out of its treasury to manufacture spyglasses that could be sent through ambassadorial channels to the major courts of Europe."

Several astronomers, such as Thomas Harriot, Joseph Gaultier de la Vatelle, Nicolas-Claude Fabri de Peiresc, and Simon Marius, published their confirmation of the Medicean Stars after Jupiter became visible again in the autumn of 1610. Marius, a German astronomer who had studied with Tycho Brahe, was the first to publish a book of his observations. Marius attacked Galileo in Mundus Jovialis (published in 1614) by insisting that he had found Jupiter’s four moons before Galileo and had been observing them since 1609. Marius believed that he therefore had the right to name them, which he did: he named them after Jupiter’s love conquests: Io, Europa, Ganymede, and Callisto. But Galileo was not confounded —- he pointed out that being outside the Church, Marius had not yet accepted the Gregorian calendar and was still using the Julian calendar. Therefore, the night Galileo first observed Jupiter's moons was January 7, 1610 on the Gregorian calendar -— December 28, 1609 on the Julian calendar (Marius claimed to have first observed Jupiter’s moons on December 29, 1609)[10] Although Galileo did indeed discover Jupiter’s four moons before Marius, Io, Europa, Ganymede, and Callisto are now the names of Galileo’s four moons.

Controversy with the Church[edit]

Galileo’s drawings of an imperfect moon directly contradicted Ptolemy’s and Aristotle’s cosmological descriptions of perfect and unchanging heavenly bodies made of quintessence (the fifth element in ancient and medieval philosophy of which the celestial bodies are composed).

Before the publication of Sidereus Nuncius, the Church accepted the Copernican heliocentric system as strictly mathematical and hypothetical.[12] However, once Galileo began to speak of the Copernican system as fact rather than theory, it introduced “a more chaotic system, a less-than-godly lack of organization.”[13] In fact, the Copernican system that Galileo believed to be real challenged the scripture, "which referred to the sun ‘rising’ and the earth as ‘unmoving.’"[13]

The conflict between Galileo and the Church ended in 1633 with his being sentenced to a form of house arrest by the Church.[1]



  • Albert Van Helden (Professor Emeritus of History at Rice University[14]); translation with introduction, conclusion and notes. Galileo Galilei, Sidereus Nuncius, or The Sidereal Messenger. Chicago and London: The University of Chicago Press, 1989. xiii + 127 pp. ISBN 978-0226279039.
  • William R. Shea and Tiziana Bascelli; translated from the Latin by William R. Shea, introduction and notes by William R. Shea and Tiziana Bascelli. Galileo’s Sidereus Nuncius or Sidereal Message. Sagamore Beach, MA: Science History Publications/USA, 2009. viii + 115 pp. ISBN 978-0-88135-375-4.
  • Stillman Drake. Telescopes, Tides, and Tactics: A Galilean Dialogue about The Starry Messenger and Systems of the World, including translation of Galileo’s Sidereus Nuncius. London: University Of Chicago Press, 1983. 256 pp. ISBN 978-0226162317.
  • Stillman Drake. Discoveries and Opinions of Galileo, includes translation of Galileo's Sidereus Nuncius. Doubleday: Anchor, 1957. 320 pp. ISBN 978-0385092395.


  • Isabelle Pantin. Sidereus Nuncius: Le Messager Celeste. Paris: Belles Lettres, 1992. ASIN B0028S7JLK.


  1. ^ a b c Raphael, Renée. Sidereus nuncius; or, A Sidereal Message, by Galileo Galilei. Isis, Vol. 101, No. 3 (September 2010), pp. 644-645. Published by: The University of Chicago Press on behalf of The History of Science Society.
  2. ^ Rosen, Edward. The Title of Galileo's Sidereus nuncius. Isis, Vol. 41, No. 3/4 (Dec., 1950), pp. 287-289. Published by: The University of Chicago Press on behalf of The History of Science Society.
  3. ^ Topping, Alexandra (2010-12-02). "Christie's New York - Beautiful Evidence: The Library of Edward Tufte Lot 13". 
  4. ^ Thomas Harriot preceded him by several months. See Telescope400
  5. ^ Righini, A. The telescope in the making, the Galileo first telescopic observations, 2010. Proceedings Of The International Astronomical Union, Volume 6 Issue 269, pp. 27-32.
  6. ^ a b c d Byard, M. M. A New Heaven: Galileo and the Artists, 1988. History Today, 38(2), 30.
  7. ^ Spiller, Elizabeth A. (2000). "Reading through Galileo's Telescope: Margaret Cavendish and the Experience of Reading". Renaissance Quarterly (The University of Chicago Press on behalf of the Renaissance Society of America) 53 (1): 192–221. doi:10.2307/2901537. 
  8. ^ Galileo trans Carlos, 1880, p45.
  9. ^ Galileo trans Carlos, 1880, p47.
  10. ^ a b c d Mendillo, M. The Appearance of the Medicean Moons in 17th Century Charts and Books—How Long Did It Take?, 2010. Proceedings Of The International Astronomical Union, 6(S269), 33.
  11. ^ Moran, B. Sidereus-Nuncius, or the Sidereal Messenger - Galilei, G, n.d. Annals Of Science, 47(5), pp. 525-526.
  12. ^ Gattei, Stefano. Book Reviews on the History of Science, Dec. 2012. Museo Galileo.
  13. ^ a b [1] Sparknotes.
  14. ^ [2] Faculty page.

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