Galileo Galilei
Galileo Galilei was an Italian physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

, mathematician
A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

, astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

, and philosopher who played a major role in the Scientific Revolution
Scientific revolution
The Scientific Revolution is an era associated primarily with the 16th and 17th centuries during which new ideas and knowledge in physics, astronomy, biology, medicine and chemistry transformed medieval and ancient views of nature and laid the foundations for modern science...

. His achievements include improvements to the telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 and consequent astronomical observations and support for Copernicanism
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....

. Galileo has been called the "father of modern observational astronomy
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...

", the "father of modern physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

", the "father of science", and "the Father of Modern Science".

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus
Phases of Venus
The phases of the planet Venus are the different variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them were telescopic observations by Galileo Galilei in 1610...

, the discovery of the four largest satellites of Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 (named the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

 in his honour), and the observation and analysis of sunspots.

1609    Galileo Galilei demonstrates his first telescope to Venetian lawmakers.

1610    Galileo Galilei observes three of the four largest moons of Jupiter for the first time. He named them, and in turn the four are called the Galilean moons. Ganymede not discovered by him until January 13.

1610    Galileo Galilei discovers Ganymede, 4th moon of Jupiter.

1612    Galileo Galilei becomes the first astronomer to observe the planet Neptune, although he mistakenly catalogued it as a fixed star.

1632    Galileo's ''Dialogue Concerning the Two Chief World Systems'' is published.

1633    Galileo Galilei arrives in Rome for his trial before the Inquisition.

1633    The formal inquest of Galileo Galilei by the Inquisition begins.

1633    The Holy Office in Rome forces Galileo Galilei to recant his view that the Sun, not the Earth, is the center of the Universe.

1633    Galileo Galilei is tried before the Congregation for the Doctrine of the Faith for teaching that the Earth orbits the Sun.


What has philosophy got to do with measuring anything? It's the mathematicians you have to trust, and they measure the skies like we measure a field.

"Matteo" in Concerning the New Star (1606)

My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh, or shall we cry?

Letter to Johannes Kepler (1610), as quoted in The Crime of Galileo (1955) by Giorgio De Santillana

See now the power of truth; the same experiment which at first glance seemed to show one thing, when more carefully examined, assures us of the contrary.

Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638); Discorsi e dimostrazioni matematiche, intorno à due nuove scienze, as translated by Henry Crew and Alfonso de Salvio (1914)

You cannot teach a man anything, you can only help him to find it within himself.

As quoted in How to Win Friends and Influence People (1935) by Dale Carnegie, p. 117; also paraphrased as "You cannot teach a man anything, you can only help him to find it for himself."

I have never met a man so ignorant that I could not learn something from him.

As quoted in The Story of Civilization : The Age of Reason Begins, 1558-1648 (1935) by Will Durant, p. 605