---
title: "Galileo Galilei"
chunk: 12/13
source: "https://en.wikipedia.org/wiki/Galileo_Galilei"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:02:33.342669+00:00"
instance: "kb-cron"
---

the Galilean moons
the roughness of the Moon's surface
the existence of a large number of stars invisible to the naked eye, particularly those responsible for the appearance of the Milky Way
differences between the appearances of the planets and those of the fixed stars—the former appearing as small discs, while the latter appeared as unmagnified points of light
Galileo published a description of sunspots in 1613 entitled Letters on Sunspots suggesting the Sun and heavens are corruptible. The Letters on Sunspots also reported his 1610 telescopic observations of the full set of phases of Venus, and his discovery of the puzzling "appendages" of Saturn and their even more puzzling subsequent disappearance. In 1615, Galileo prepared a manuscript known as the "Letter to the Grand Duchess Christina" which was not published in printed form until 1636. This letter was a revised version of the Letter to Castelli, which was denounced to the Inquisition by Niccolò Lorini (as discussed previously). In 1616, after the order by the Inquisition for Galileo not to hold or defend the Copernican position, Galileo wrote the "Discourse on the Tides" (Discorso sul flusso e il reflusso del mare) based on the Copernican earth, in the form of a private letter to Cardinal Orsini. In 1619, Mario Guiducci, a pupil of Galileo's, published a lecture written largely by Galileo under the title Discourse on the Comets (Discorso Delle Comete), arguing against the Jesuit interpretation of comets.
In 1623, Galileo published The Assayer (Il saggiatore), which attacked theories based on Aristotle's authority and promoted experimentation and the mathematical formulation of scientific ideas. The book was highly successful; Pope Urban was "so charmed by it as to have it read aloud to him at table." Following the success of The Assayer, Galileo published the Dialogue Concerning the Two Chief World Systems (Dialogo sopra i due massimi sistemi del mondo) in 1632. Despite taking care to adhere to the Inquisition's 1616 instructions, the claims in the book favouring Copernican theory and a non-geocentric model of the solar system led to Galileo being tried and banned from publication. Despite the publication ban, Galileo published his Discourses and Mathematical Demonstrations Relating to Two New Sciences (Discorsi e Dimostrazioni Matematiche, intorno a due nuove scienze) in 1638 in Holland, outside the jurisdiction of the Inquisition.

=== Published written works ===
Galileo's main written works are as follows:

The Little Balance (1586; in Italian: La Bilancetta)
On Motion (c. 1590; in Latin: De Motu Antiquiora)
Mechanics (c. 1600; in Italian: Le Mecaniche)
The Operations of Geometrical and Military Compass (1606; in Italian: Le operazioni del compasso geometrico et militare)
The Starry Messenger (1610; in Latin: Sidereus Nuncius)
Discourse on Floating Bodies (1612; in Italian: Discorso intorno alle cose che stanno in su l'acqua, o che in quella si muovono, "Discourse on Bodies that Stay Atop Water, or Move in It")
History and Demonstration Concerning Sunspots (1613; in Italian: Istoria e dimostrazioni intorno alle macchie solari; work based on the Three Letters on Sunspots, Tre lettere sulle macchie solari, 1612)
"Letter to the Grand Duchess Christina" (1615; published in 1636)
"Discourse on the Tides" (1616; in Italian: Discorso del flusso e reflusso del mare)
Discourse on the Comets (1619; in Italian: Discorso delle Comete)
The Assayer (1623; in Italian: Il Saggiatore)
Dialogue Concerning the Two Chief World Systems (1632; in Italian: Dialogo sopra i due massimi sistemi del mondo)
Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638; in Italian: Discorsi e Dimostrazioni Matematiche, intorno a due nuove scienze)