Editing Sidereus Nuncius (section)

==Content==
[[File:Galileo's sketches of the moon.png|thumb|200px|right|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 (constellation)|Orion]], the [[Pleiades]], and [[Taurus (constellation)|Taurus]], and the [[Galilean moons|Medicean Stars]] of Jupiter. Galileo's text also includes descriptions, explanations, and theories of his observations.

===Moon===
In observing the Moon, Galileo saw that the line separating lunar day from night (the [[Lunar terminator|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.<ref name="larb2014"/> 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 [[engraving]]s 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.<ref name="Raphael"/>

[[File:Pleiades Sidereus Nuncius.png|thumb|left|200px|Galileo's drawings of the Pleiades star cluster from ''Sidereus Nuncius''.]]

===Stars===
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 [[Pleiades]]; 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.<ref name="Spiller">{{cite journal |last=Spiller |first=Elizabeth A. |title=Reading through Galileo's Telescope: Margaret Cavendish and the Experience of Reading |journal=[[Renaissance Quarterly]] |volume=53 |issue=1 |year=2000 |pages=192–221 |doi=10.2307/2901537 |jstor= 2901537|s2cid=191407323 |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1215&context=englishfacpubs }}</ref> Also, when he observed some of the "nebulous" stars in the [[Ptolemy|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.<ref name="Byard" />

===Medicean Stars (Moons of Jupiter)===
[[File:Medicean Stars.png|200px|right|thumbnail|Galileo's drawings of Jupiter and its Medicean Stars from ''Sidereus Nuncius.'']]

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.<ref>[https://archive.org/stream/siderealmessenge80gali#page/44/mode/2up Galileo trans Carlos], 1880, p45.</ref><ref name="larb2014"/> 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 four 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.<ref>Galileo trans Carlos, 1880, p47.</ref>

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."<ref name="Mendillo">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.</ref>

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, now 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 [[House of Medici|Medici]] brothers.<ref name="larb2014"/> This helped him receive the position of Chief Mathematician and Philosopher to the Medici at the University of Pisa.<ref name="Byard" /> Ultimately, his effort at naming the moons failed, for they are now referred to as the "[[Galilean moons]]".