Galileo Galilei

Many believe that Galileo is "the father of modern science." He was an exceptional mathematician, astronomer, and physicist.

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Galileo Demonstrating the New Astronomical Theories at the University of Padua (1873) by Félix ParraMuseo Nacional de Arte

Galileo was among the first explorers of space, using a telescope and interpreting what he saw as evidence in support of the idea that the earth revolves around the sun and is not the center of the universe, scandalous for his time. 

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So it is no wonder that Galileo is sometimes considered the founder of modern experimental science!


Galileo was born in Pisa, Italy, where he grew up with his brothers and sisters during the Italian Renaissance. His father was a music teacher and a famous musician. His family moved to the city of Florence when he was 10 years old.

It was in Florence that Galileo began his education at the Camaldolese monastery.

Interesting Facts

Galileo was an accomplished musician and an excellent student. He enrolled to get a medical degree at the University of Pisa but never finished, instead choosing to become a teacher and experiment with ramps, pendulums, levers, balls, and other objects.


In 1609, Galileo heard of an invention from Holland, called the telescope, that could make far away items appear much closer. He decided to build his own telescope. He made great improvements to it and directed it to the stars.

E pur si muove!

Аs Galileo studied the planets and the Sun, he became convinced that the Earth and the other planets orbited the Sun. In 1632, he described these ideas. However, the powerful Catholic Church considered Galileo's ideas as heresy and forced him to confess.

Galileo’s Lamp

Galileo conducted his first observations and experiments as a student at the University of Pisa. The huge Cathedral of Pisa, an architectural masterpiece from the 11th century served as his first "laboratory."

His subject of research? A chandelier that remains known to history as the "Lamp of Galileo."

The Lamp

The 19-year-old Galileo watched the suspended lamp swing back and forth, and he discovered the Law of Isochronism. It states that a pendulum takes the same time to complete a swing no matter how big the swing is.

The Swing of the Pendulum

A sudden breeze or an accidental nudge would sway the lamp with a varying amplitude. Galileo noticed that, regardless of the fluctuation, the period of oscillation of the pendulum lamp would remain constant. 

Inner Clock

To prove this, Galileo needed an instrument to measure time. He had an idea: his own pulse. Later, he proposed that the fluctuations of the pendulum would be used to measure small time intervals, and created a clock project, based on measured pendulum movement.

The Eye of Genius

At first glance, the swinging of the lamp is an insignificant phenomenon. In Galileo's observations, however, it played a role as significant as Archimedes' bathtub and Newton's apple. The genius was able to see in ordinary events what millions had not seen before him.

The Myth of the Tower of Pisa

Galileo discovered the Law of Inertia that states that all objects released together fall at the same rate regardless of their mass. This means that gravity pulls on all objects equally. 

Of course, actually performing an experiment to prove that in the year 1600 would have been difficult due to air resistance and the technology of the times.

Debunked: The Tower of Pisa Myth

Don’t believe in fables that say Galileo dropped cannonballs and bird feathers off the Leaning Tower of Pisa to compare their time of fall. In fact, most historical records indicate that Galileo himself probably never performed this experiment, although he discussed the ideas.

Hammer-Feather Drop in Space

During the Apollo 15 moonwalk, astronaut David Scott dropped a hammer and a feather at the same time. Because they were in a vacuum, with no air resistance, they fell at the same rate, as Galileo had concluded hundreds of years earlier.

Galileo’s Telescope

Galileo is often considered the man who invented the telescope. This is not so. He did not invent it, but he was the first one who pointed it to the cosmos. 

The observations he made created the science of modern astronomy, which uses telescopes that help us understand our universe, our place in it, and the way it works.

The Telescope

Galileo first heard about the telescope in 1609 and decided to make a copy for himself with around 3x magnification. For more than a decade, he continued to create more telescopes and finally invented one with around 30x magnification.

Galileo’s First Object

The first object towards which Galileo turned his telescope was the moon. On its surface, he saw shadows cast by craters and mountains. This was an incredibly important discovery because it was previously believed that the moon had a smooth surface.

Jupiter’s Moons

One night, Galileo pointed his telescope towards Jupiter, and saw a peculiar sight: 2 tiny "stars" to the east of Jupiter, and 1 to the west, all arranged in a tight straight line along the ecliptic path with Jupiter itself.

Galileo made a sketch of this unusual "chance" alignment of celestial objects. 

Galileo’s Whim

The next evening, on a whim, Galileo decided to check that the 3 "fixed stars" lay to the east of Jupiter, since he knew that the planet was moving westward in its retrograde motion. Sure enough, there were the 3 stars again, but on the west!

Jupiter’s Moons

The only explanation was that the stars were not "fixed" at all, but moved with Jupiter, and, indeed, seemed to move around it like our own moon moves around the Earth. This was the beginning of the end of the geocentric universe. 

Four Moons

Galileo actually saw all 4 moons, but was unable to resolve Io and Еuropa, which were very close together at the time. Galileo published his notes in a book where he named the satellites after his patrons, 4 brothers of the Medici family.

Zeus’ Lovers

German astronomer Simon Marius, however, proposed that they should be named Io, Europa, Callisto, and Ganymede — the 4 lovers of Zeus whose equivalent Roman god was Jupiter. Allegedly, Marius discovered the moons first, but his publication was delayed.

Galileo and the Inquisition

Unfortunately, a long conflict with the clergy turned his career as a prominent scientist into a drama. How and why did it start? In Galileo's time, many people believed in a geocentric universe where all heavenly objects revolved around the earth.

Galileo's discovery of moons orbiting Jupiter disproved that theory.

Heliocentrism and Catholicism

While Galileo's discovery did not prove the earth travels around the sun, it disagreed with the way many people interpreted the Bible.

In 1616, Pope Paul V, the leader of Galileo's Catholic Church, commanded that the scientist never again "defend or hold" the idea of a heliocentric universe.

The Heresy

Although deeply religious, Galileo continued to make new discoveries and to promote Copernicus' theory of a universe that revolved around the sun. Galileo later went on trial for heresy. Heresy is an opinion or belief that disagrees with the official position of the Church.

The Sentence

The Church found Galileo guilty and sentenced him to house arrest for the remaining 9 years of his life. He accepted his sentence, but he continued to write and study. By legend (not fact), Galileo whispered to himself after his confession, “And yet it moves!”

The Confession

In his confession, Galileo said he abandoned “the false opinion which maintains that the Sun is the centre and immovable.” Some historians claim that the humiliation of denying his discoveries tormented the scientist for the rest of his life.

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