Galileo Galilei: Starry Messenger

Explanation and Analysis of the Document

The text emphasizes the greatness of Galileo’s discoveries and the amazement that they would provoke in the reader also because of the instrument that made them possible. A cursory look at the first paragraphs immediately reveals this sense of wonder that the author wants to create in the reader thanks to the use of words such as “great” (repeated later in the text), “novelty,” and “excellence.” Employing a telescope, Galileo was able to discover a high number of fixed stars, mountains and valleys on the moon, the true nature of “nebulous” stars, and the “four wandering planets” around Jupiter. After summarizing the most important discoveries that constitute the topic of his treaty, the scientist goes on to explain how he constructed the instrument that made such discoveries possible: the telescope. Although he thinks that its application could be useful both on land and sea, he says that he has limited its use to celestial observations.

According to his report, Galileo first heard about the instrument ten months before the writing of the Starry Messenger. Although there was no consensus about the benefits of the instrument, the Italian scientists decided to construct one. This passage is typical of the Galilean scientific method in several respects. Galileo does not simply accept that the instrument is useful or useless because other people have said so. He proceeds to verify personally other people’s opinions. This empirical validation is one of Galileo’s major contributions to scientific enquiry. Following from this, Galileo thought that everyone should be able to replicate experiments made by other scientists, to prove them right or wrong. For this reason, he tells of the different steps that he took in the construction of the telescope, allowing everyone to try to construct one to observe the same things that he is writing about. Galileo is clearly speaking to those potential scientists (“to all who intend to turn their attention to observations of this kind”) when he warns them that their telescope should be able to magnify the things they observe by at least four hundred times.

After explaining the construction and use of the telescope, Galileo delves into more details about his celestial observations. The majority of the document is devoted to his observations of the moon, while its concluding paragraphs focus on stars and the nature of the Milky Way. The Italian scientist addresses his description of the moon to “all who are eager for true philosophy,” because the Aristotelian and medieval cosmology was predicated on the qualitative difference between the earth, rugged and irregular, with mountains, valleys, and caves, and perfect celestial bodies like the moon, “smooth, free from inequalities, and exactly spherical.” This qualitative difference implied a moral superiority of the celestial bodies because of their perfection and the inferiority of the earth because of its imperfections. Yet Galileo was able to prove that this qualitative difference did not exist, as the moon, too, was “full of inequalities, uneven, full of hollows and protuberances, just like the surface of the Earth itself, which is varied everywhere by lofty mountains and deep valleys.”

This conclusion is reinforced by Galileo’s style, which draws constant parallels between what happens on the moon and terrestrial phenomena or uses everyday objects as metaphors to illustrate his conclusions. For example, when talking about the lunar spots, he recalls that “we have an appearance quite similar on Earth about sunrise.” In a passage devoted to the moon’s surface, he argues that “it is marked with spots like a peacock’s tail with its azure eyes” and resembles “those glass vases which … acquire a crackled and wavy surface.” These lexical choices show Galileo’s aim to democratize the language of science, making it accessible not only to philosophers and highly educated theologians but also to those people who were genuinely interested in the subject.