Men Who “See” Stars

by Piergiorgio ODIFREDDI

On January 7, 1610, Galileo wrote a letter to Antonio de’ Medici where he briefly reported on the results of his first observations of the sky through a telescope exactly 400 years ago, late in the summer of 1609. The letter con­cluded with some news of the day: “Only this evening I have seen Jupiter accompa­nied by three fixed stars totally invisible because of their smallness.” With under­standable and justifiable pride, he also noticed: “We can believe to have been the first in the world to discover some­thing about the heavenly bodies from so nearby and so distinctly.”

It was the first historical hint of the discoveries that were to be announced in great detail to the entire world later on March 12, in his first great scientific treatise – Sidereus Nuncius, “The Starry Message (or Messenger),” where Jupi­ter’s satellites were given the name of Medicean Stars. As Galileo immediately understood, this discovery definitively disproved the centrality of the Earth in the planets’ movement, and therefore could, and should, open the way to the acceptance of Copernican theory.

Immediately, Galileo sent a copy of his Sidereus Nuncius to Kepler, asking for his opinion.  Kepler   received it on April 8, 1610. In only eleven days, he sent him back his Conversation with the Starry Messenger, where he defended and supported Galileo, even if he criti­cized the fact that Galileo pretended to have done everything all alone without even mentioning the names of his prede­cessors (except for Copernicus).

Ungrateful, Galileo did not even con­descend to Kepler’s request for an instrument that would allow him to personally check his findings. Kepler had to wait until August 1611 before he could get one. As soon as he got it, in ten days of observation he confirmed the existence of Medicean Stars, and profusely and immediately wrote his Narration about Four Satellites of Jupiter Observed in or­der to testify it.

Even before Kepler’s Narration, Galileo had been given significant scientific recognition from the mathematicians of the Jesuit Roman College, whom he had visited in the spring of 1611. They received him with all honours, and praised his Sidereus Nuncius in a public discourse. In Rome noblemen and prel­ates also acclaimed the Tuscan scientist: in particular, Prince Federico Cesi made him a member of his Lincean Academy, which he had founded in 1603, and Pope Paul V released him from the obligation to kneel down before him during an au­dience.

However, not everybody accepted these new findings so eagerly. In a letter sent out to Father Christophorus Clavius on May 27, 1611, a certain Ludovico delle Colombe, for example, clutched at straws claiming that the Moon seemed to be rough and uneven, just like the surface of the Earth itself, but in fact it was “a large crystal ball in which were contained many kinds of figures made of white enamel.”

In a letter written to Gallanzone Gal­lanzoni on July 16, 1611, amused, Galileo replied that if we still want to let any­one imagine whatever he pleases, and if someone says that the moon is spheri­cally surrounded by transparent invisible crystal, then he would willingly grant this – provided that with equal courtesy it is permitted to him to say that this crystal has on its outer surface a great number of enormous mountains, thirty times as high as terrestrial ones.

In the meantime, he had already gone beyond his Sidereus Nuncius with his discoveries. In a letter from July 30, 1610, he informed Belisario Vinta that “the star of Saturn is not a single one, but is a composite of three, which almost touch each other, never change or move relative to each other.” Galileo encoded his inter­pretation of this “very strange wonder” as a Latin anagram, which he posted to G i u l i a n o   d e ’  M e d i c i   a n d   K e p l e r :   s m a ­ismrmilmepoetaleumibunenugttauiras, which was to be unscrambled as altissi­mum planetam tergeminum observavi, meaning “I have observed the highest planet to have a triple form.”

Galileo was induced to believe that Saturn had a “triple form” because his 20-power telescope was not powerful enough. With a 50-power telescope, in 1655, Christian Huygens would discover that the planet is surrounded by a thin flat ring, and that it also has a satellite, which he would name Titanus. In 1671 Giovanni Cassini would also discover two other satellites, Iapetus and Rhea, and would realize that Saturn has more than one ring, and that these rings are concentric and coplanar. Hence the name of the Cassini-Huygens spacecraft, which has been orbiting Saturn since 2004.

Going back to Galileo, in September 1610, he moved from Padua to Florence, where he was given the title as “Chief Mathematician of the University of Pisa and Philosopher to the Grand Duke,” holding a chair that all professors would dream about: he had not to hold lectures or carry out examinations, but he could entirely dedicate himself to his research. Scrupulously, the scientist continued his observations, and on December 11, 1610, he announced his new discovery to Giu­liano de’ Medici through another ana­gram: haec immatura a me iam frustra leguntur oy, meaning “these immature ones have already been read in vain by me,” that is, when rearranged, Cynthiae figuras aemulatur Mater Amorum (Latin: “the Mother of Loves [= Venus] imitates the figures of Cynthia [= the moon]).

Kepler tried to decode both this and the first weird announcement concealed by “transposed letters.” The solutions he proposed in both cases were wrong in Galileo’s perspective, but they proved to be correct in the light of further scientific developments. To be more precise, the first anagram – salve umbistineum gemi­natum Martas proles, meaning “Hello, furious twins, sons of Mars” – antici­pated the discovery of the two satellites of Mars (Phobos and Deimos) in 1877. Whereas, the second one – macula rufa in Iove est gyratur mathem etc., that is “there is a red spot on Jupiter, that turns mathematically” – anticipated the discov­ery of a “permanent spot” detected by Cassini in 1665 and visible until 1713, and of the Great Red Spot, which was (re)discovered in the 19th Century and is still visible today.

As for the phases of Venus, in a let­ter addressed to Giuliano de’ Medici in January 1, 1611, Galileo stated that it was not a proper discovery, but it was more like “seeing with his own eyes what his in­tellect had no doubt about”: according to the heliocentric theory, in fact, all plan­ets revolve around the Sun, in the same manner as the Moon revolves around the Earth.

Both Galileo and Kepler were actually able to see, with the eye of mind, well beyond what they could with their physi­cal eyes through the telescope. Neither of them had the chance to personally go to the Moon to see what the Earth looked like from there, but nevertheless they both described the sight of it in their books: respectively, in the first day of The Dialogue Concerning the Two Chief World Systems, and in the science-fiction novel Somnium (The Dream).

The multicoloured results of their imagination – which have been con­firmed today by the observations and photographic records of the astronauts who set foot on the moon for the first time exactly forty years ago – go beyond any poetic invention. On the one hand, in fact, the Earth goes through phases in the Moon’s sky that are equal and contrary to those of the Moon in the Earth’s sky. On the other hand, since the Moon always shows the same face to the Earth, the Earth can only be seen from the part of the Moon that is visible to us, and from there it appears fixed in the sky. This means that whoever might happen to walk on the visible surface of the Moon in a period of full Earth could observe “this fatal globe,” immobile in the lunar sky, rotating on itself every 24 hours. In front of such wonderful visual demonstration of the rotatory motion of the Earth, a self-conscious lunar poet would exclaim: “what are you doing, earth in heaven? Tell me? What are you doing, silent earth?”

The terrestrial poets of unconscious, instead, know only one thing about the moon: that it exists. Even the amateurs of astronomy do not know much more than that. In 1819, Giacomo Leopardi, who greatly appreciated Galileo, was still writing about the Moon that “no one’s ever seen it fall, except in dreams” (Canti, XXXVII, 17-18), even if in 1687 Isaac Newton had composed the verse “the Moon continuously falls in its path around the Earth” (Principia, III, 4), and had also calculated exactly how much it falls by: the very same force that makes an apple fall from the tree also keeps the Moon on its orbit around the Earth. This demonstrates that there is much more poetry in science books than in the an­thologies of the men of letters, and that it is not enough to look at and admire the sky to really see and understand it.

About the Author


Piergiorgio Odifreddi has studied mathematics and logic in Italy, the United States and the Soviet Union, and has taught it in Italy (University of Turin) and the United States (Cornell University). He writes for many newspapers and magazines, from Repubblica and L’Espresso to Le Scienze. In 1998 he received the Galileo Prize of the Italian Mathematical Union, in 2002 the Peano Prize of Mathesis, and in 2006 the Italgas Award for the Popularization of Science. Among his books translated into English: The Mathematical Century (Princeton University Press, 2004).