Galileo Observing Challenge

Lunar Image sketch

On the last day of November, 1609, Galileo trained a 20x-perspective glass on the moon, and was rewarded with the sight of lunar sunrise over the Janssen walled plain. This was the beginning of his intensive period of telescopic astronomical discovery. The Paduan professor's observing programmes became possible through his refinement of the telescope, the interpretative acuity of his eye and mind, and the acquired proficiency of his hand. Galileo's ability to draw startlingly important conclusions from his observations, and his skill at their broadcast helped mould modern astronomy. Four centuries later his achievements and our ever-changing relationship to them form a principal theme of the International Year of Astronomy. The image of Galileo as a hands-on natural philosopher suggests active involvement in IYA2009, which at its best becomes a spectacle with no passive viewing from the sidelines: a Galileo moment, whatever form it may take, is an act of observing.

In that spirit, the RASC Astrosketchers' Forum is sponsoring a "Galileo Observing Challenge", to encourage any RASC member to enter into active dialogue with any portion of Galileo's early telescopic observing work. This project was developed at the prompting of Barry Matthews, based on a suggestion of Gary Seronik's in the 2008 SkyWatch. The principal is simple, the rules few.

  • Do your own hand-drawn image(s) of any of the objects Galileo reported in his Sidereus nuncius (the moon, or Jupiter and its four largest moons [the "Medicean stars"], the Pleiades, the Praesepe (Beehive) cluster, and the objects around the belt, sword and the rest of Orion), use any optical means you like - provided that the combined magnification of your system is between 3x and 30x - like those employed by Galileo, and submit electronic jpegs of your images at 300dpi to by September 1, 2009 with the subject heading Galileo Observing Challenge.
  • Include a description of the object(s), the optical means used (aperture, focal length,and magnification), and most importantly, what you experienced, learned, or grasped in active dialogue with the first printed telescopic astronomical images. Your reflection could be any length, from a three word sentence to a thousand word mini-essay, whichever seems right to you. You could report on what it is like to try to limit yourself in some way to the instrumental conditions of an early 17th-century observer, or on the experience as a way to approach Galileo as a fellow observer, or on an insight into what Galileo was able to accomplish, or how contemplating his observations allows you to see familiar objects in a different light.
  • The image can be in any hand-produced medium; pencil and paper, crayon, chalk, watercolour, charcoal, pen and ink, acrylic, woodcut, engraving, lino-cut, collage, stained glass, etc. You can make the project as simple or as creative as you like. You can use any modern telescope (or binoculars or opera glasses) you already own, or you can use a reconstruction of a Galilean telescope. Likewise, the style and technique of your image can be thoroughly twenty-first century, or you can use the techniques and materials available to Galileo, or anything in between.

All the entries with descriptions will be put on the website after the "Galileo Observing Challenge" closes. A selection from the entries received before June 1 may be used for an exhibition at the 2009 General Assembly August 13-16 at Cypress Hills Interprovincial Park.

Accept the Galileo Observing Challenge, and interact with the rich cultural heritage of astronomical history to explore the present!



  • an autograph manuscript of the Sidereus nuncius, with Galileo's original wash drawings tipped in, is available online: go to This manuscript was rebound in the nineteenth century, and may have been compiled at that period from autograph copies by Galileo and his assistants. The wash drawings (divorced from their manuscript context) were formerly available at:

Several digital facsimiles of the 1610 printed editions are online:

  • for the Venice edition, Galileo Galilei, Sidereus nuncius... (Venice: apud Thomam Baglionum, 1610), use the same search engine as for the Florence manuscript above (but don't click on the manuscript button, of course!)
  • the Frankfurt edition, Galileo Galilei, Sidereus nuncius... (Frankfurt: Prostat in Paltheniano, 1610), is even easier to access:


  • the best English translation is the authoritative Galileo Galilei, Siderius nuncius or the Sidereal Messenger, tr. Albert van Helden (Chicago: University of Chicago Press, 1989: ISBN 0226279030)
  • a late-19th century translation, markedly less good than van Helden's, is online: Galileo Galilei, The Sidereal Messenger, tr. Edward Stafford Carlos (Oxford-Cambridge-London: Rivington's, 1880):


  • the fullest accounts are: Horst Bredekamp, "Gazing Hands and Blind Spots: Galileo as Draftsman" in Science in Context vol. 14 (2001), 153-192: and Horst Bredekamp, Galileo der Künstler: die Mond-die Sonne-die Hand (Berlin: Akademie Verlag, 2007). Those interested should also read the contributions by van Helden, Gingerich, Winkler, and Edgerton cited by Bredekamp.
  • for the context of Galileo's lunar drawings within the developing traditions of selenography see: Ewen A. Whitaker, "Selenography in the Seventeenth Century", in Planetary Astronomy from the Renaissance to the Rise of Physics.Renaissance to the Rise of Physics. Part A: Tycho Brahe to Newton, ed. René Taton and Curtis Wilson, The General History of Astronomy, ed. Micahel Hoskin, vol. 2 (Cambridge: Cambridge University Press, 1989), pp. 119-143, and Ewen A. Whitaker, Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature (Cambridge: Cambridge University Press, 1999). For a dissenting view that: a) the manuscript wash drawings may not be by Galileo; and b), that the published illustrations in Sidereus nuncius are wholly impressionistic, search for T Pope's notes, formerly at: Note that this is very much a minority opinion on both issues.


  • two enlightening accounts presenting Galileo's instruments within their cultural contexts are: Mario Biagioli, Galileo's Instruments of Credit: Telescopes, Images, Secrecy (Chicago: University of Chicago Press, 2006), and Eileen Reeves, Galileo's Glassworks: the Telescope and the Mirror (Cambridge MA-London: Harvard University Press, 2008).
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Saturday, November 4, 2017 - 8:45am