Biography of Galileo Galilei
By Mary Bellis, About.com Guide
Galileo Galilei was born in Pisa, Italy on February 15, 1564. He
was the oldest of seven children. His father was a musician and wool
trader, who wanted his son to study medicine as there was more money
in medicine. At age eleven, Galileo was sent off to study in a Jesuit
Galileo Galilei - Rerouted from Religon to Science
After four years, Galileo had announced to his father that he wanted
to be a monk. This was not exactly what father had in mind, so
Galileo was hastily withdrawn from the monastery. In 1581, at the
age of 17, he entered the University of Pisa to study medicine,
as his father wished.
Galileo Galilei - Law of the Pendulum
At age twenty, Galileo noticed a lamp swinging overhead while he
was in a cathedral. Curious to find out how long it took the lamp
to swing back and forth, he used his pulse to time large and small
swings. Galileo discovered something that no one else had ever
realized: the period of each swing was exactly the same. The law
of the pendulum, which would eventually be used to regulate clocks,
made Galileo Galilei instantly famous.
Except for mathematics, Galileo Galilei was bored with university.
Galileo's family was informed that their son was in danger of flunking
out. A compromise was worked out, where Galileo would be tutored
full-time in mathematics by the mathematician of the Tuscan court.
Galileo's father was hardly overjoyed about this turn of events,
since a mathematician's earning power was roughly around that of
a musician, but it seemed that this might yet allow Galileo to successfully
complete his college education. However, Galileo soon left the University
of Pisa without a degree.
Galileo Galilei - Mathematics
To earn a living, Galileo Galilei started tutoring students in mathematics.
He did some experimenting with floating objects, developing a balance
that could tell him that a piece of, say, gold was 19.3 times heavier
than the same volume of water. He also started campaigning for his
life's ambition: a position on the mathematics faculty at a major
university. Although Galileo was clearly brilliant, he had offended
many people in the field, who would choose other candidates for vacancies.
Galileo Galilei - Dante's Inferno
Ironically, it was a lecture on literature that would turn Galileo's
fortunes. The Academy of Florence had been arguing over a 100-year-old
controversy: What were the location, shape, and dimensions of Dante's
Inferno? Galileo Galilei wanted to seriously answer the question
from the point of view of a scientist. Extrapolating from Dante's
line that "[the giant Nimrod's] face was about as long/And
just as wide as St. Peter's cone in Rome," Galileo deduced
that Lucifer himself was 2,000 armlengths long. The audience was
impressed, and within the year, Galileo had received a three-year
appointment to the University of Pisa, the same university that
never granted him a degree!
The Leaning Tower of Pisa
At the time that Galileo arrived at the University, some debate had
started up on one of Aristotle's "laws" of nature, that
heavier objects fell faster than lighter objects. Aristotle's word
had been accepted as gospel truth, and there had been few attempts
to actually test Aristotle's conclusions by actually conducting
According to legend, Galileo decided to try. He needed to be able
to drop the objects from a great height. The perfect building was
right at hand--the Tower of Pisa, 54 meters tall. Galileo climbed
up to the top of the building carrying a variety of balls of varying
size and weight, and dumped them off of the top. They all landed
at the base of the building at the same time (legend says that the
demonstration was witnessed by a huge crowd of students and professors).
Aristotle was wrong.
Galileo Galilei continued to behave rudely to his colleagues, not
move for a junior member of the faculty. "Men are
like wine flasks," he once said to a group of students. "...look
at....bottles with the handsome labels. When you taste them, they
are full of air or perfume or rouge. These are bottles fit only to
pee into!"Not surprisingly, the University of Pisa chose not
to renew Galileo's contract.
Necessity is the Mother of Invention
Galileo Galilei moved on to the University of Padua. By 1593, he
was desperate in need of additional cash. His father had died, so
Galileo was the head of his family, and personally responsible for
his family. Debts were pressing down on him, most notably, the dowry
for one of his sisters, which was paid in installments over decades
(a dowry could be thousands of crowns, and Galileo's annual salary
was 180 crowns). Debtor's prison was a real threat if Galileo returned
What Galileo needed was to come up with some sort of device that
could make him a tidy profit. A rudimentary thermometer (which, for
the first time, allowed temperature variations to be measured) and
an ingenious device to raise water from aquifers found no market.
He found greater success in 1596 with a military compass that could
be used to accurately aim cannonballs. A modified civilian version
that could be used for land surveying came out in 1597, and ended
up earning a fair amount of money for Galileo. It helped his profit
margin that 1) the instruments were sold for three times the cost
of manufacture, 2) he also offered classes on how to use the instrument,
and 3) the actual toolmaker was paid dirt-poor wages.
A good thing. Galileo needed the money to support his siblings,
his mistress (a 21 year old with a reputation as a woman of easy
habits), and his three children (two daughters and a boy). By 1602,
Galileo's name was famous enough to help bring in students to the
University, where Galileo was busily experimenting with magnets.
In Venice on a holiday in 1609, Galileo Galilei heard rumors that a
Dutch spectacle-maker had invented a device that made distant objects
seem near at hand (at first called the spyglass and later renamed the
telescope). A patent had been requested, but not yet granted, and the
methods were being kept secret, since it was obviously of tremendous
military value for Holland.
Galileo Galilei - Spyglass
Galileo Galilei was determined to attempt to construct his own spyglass.
After a frantic 24 hours of experimentation, working only on instinct
and bits of rumors, never having actually *seen* the Dutch spyglass,
he built a 3-power telescope. After some refinement, he brought
a 10-power telescope to Venice and demonstrated it to a highly
impressed Senate. His salary was promptly raised, and he was honored
Galileo Galilei - The Moon
If he had stopped here, and become a man of wealth and leisure, Galileo
Galilei might be a mere footnote in history. Instead, a revolution
started when, one fall evening, the scientist trained his telescope
on an object in the sky that all people at that time believed must
be a perfect, smooth, polished heavenly body--the Moon. To his
astonishment, Galileo Galilei viewed a surface that was uneven,
rough, and full of cavities and prominences. Many people insisted
that Galileo Galilei was wrong. Some of their arguments were very
clever, like the mathematician who insisted that even if Galileo
was seeing a rough surface on the Moon, that only meant that the
entire moon had to be covered in invisible, transparent, smooth
Galileo Galilei - Jupiter
Months passed, and his telescopes improved. On January 7, 1610,
he turned his 30 power telescope towards Jupiter, and found
small, bright stars near the planet. One was off to the west,
the other two were to the east, all three in a straight line.
evening, Galileo once again took a look at Jupiter, and found
that all three of the "stars" were now west of
the planet, still in a straight line!
Observations over the following weeks lead Galileo to the
inescapable conclusion that these small "stars" were
actually small satellites that were rotating about Jupiter.
If there were satellites
that didn't move around the Earth, wasn't it possible that the
Earth was not the center of the universe? Couldn't the Copernican
of the Sun at the center of the solar system be correct?
The Starry Messenger
Galileo Galilei published his findings--as a small book titled The
Starry Messenger. 550 copies were published in March of 1610, to
tremendous public acclaim and excitement.
Galileo Galilei - Saturn
For Galileo Galilei, saying that the Earth went around the Sun changed
everything since he was contradicting the teachings of the Church.
While some of the Church's mathematicians wrote that his observations
were clearly correct, many members of the Church believed that he must
And there were more discoveries via the new telescope: the appearance
of bumps next to the planet Saturn (Galileo thought they were
companion stars; the "stars" were actually the
edges of Saturn's rings), spots on the Sun's surface (though
others had actually
seen the spots before), and seeing Venus change from a full disk
to a sliver of light.
In December of 1613, one of the scientist's friends told him how a
powerful member of the nobility said that she could not see how his
observations could be true, since they would contradict the Bible.
The lady quoted a passage in Joshua where God causes the Sun to stand
still and lengthen the day. How could this mean anything other than
that the Sun went around the Earth?
Galileo Galilei - Heresy Charges
Galileo Galilei was a religious man, and he agreed that the Bible could never
be wrong. However, he said, the interpreters of the Bible could make mistakes,
and it was a mistake to assume that the Bible had to be taken literally.
This might have been one of Galileo's major mistakes. At that time, only Church
priests were allowed to interpret the Bible, or to define God's intentions.
It was absolutely unthinkable for a mere member of the public to do so.
And some of the Church clergy
started responding, accusing him of heresy. Some credits went
to the Inquisition, the Church court that investigated charges
of heresy, and formally accused Galileo Galilei. This was a very
serious matter. In 1600, a man named Giordano Bruno was convicted
of being a heretic for believing that the earth moved about the
Sun, and that there were many planets throughout the universe
where life--living creations of God--existed. Bruno was burnt
However, Galileo was found
innocent of all charges, and cautioned not to teach the Copernican
system. 16 years later, all that would change.
The Final Trial
The following years saw Galileo move on to work on other projects. With his
telescope he watched the movements of Jupiter's moons, wrote them up as a list,
and then came up with a way to use these measurements as a navigation tool.
There was even a contraption that would allow a ship captain to navigate with
his hands on the wheel. That is, assuming the captain didn't mind wearing what
looked like a horned helmet!
As another amusement, Galileo started writing about ocean tides. Instead of
writing his arguments as a scientific paper, he found that it was much more
interesting to have an imaginary conversation, or dialogue, between three fictional
characters. One character, who would support Galileo's side of the argument,
was brilliant. Another character would be open to either side of the argument.
The final character, named Simplicio, was dogmatic and foolish, representing
all of Galileo's enemies who ignored any evidence that Galileo was right. Soon,
he wrote up a similar dialogue called "Dialogue on the Two Great Systems
of the World." This book talked about the Copernican system.
an immediate hit with the public, but not, of course, with the
Church. The pope suspected that he was the model for Simplicio.
He ordered the book banned, and also ordered the scientist to
appear before the Inquisition in Rome for the crime of teaching
the Copernican theory after being ordered not to do so.
Galileo Galilei was 68 years
old and sick. Threatened with torture, he publicly confessed
that he had been wrong to have said that the Earth moves around
the Sun. Legend then has it that after his confession, Galileo
quietly whispered "And yet, it moves."
Unlike many less famous prisoners,
he was allowed to live under house arrest in his house outside
of Florence. He was near one of his daughters, a nun. Until his
death in 1642, he continued to investigate other areas of science.
Amazingly, he even published a book on force and motion although
he had been blinded by an eye infection.
The Story Continues...
The Church eventually lifted the ban on Galileo's Dialogue in 1822--by that
time, it was common knowledge that the Earth was not the center of the Universe.
Still later, there were statements by the Vatican Council in the early 1960's
and in 1979 that implied that Galileo was pardoned, and that he had suffered
at the hands of the Church. Finally, in 1992, three years after Galileo Galilei's
namesake had been launched on its way to Jupiter, the Vatican formally and
publicly cleared Galileo of any wrongdoing.