Galileo was one of the greatest
astronomers in the world. He changed the way we think
about the universe. Galileo was the first person to
use a telescope to look at the universe. He studied
the sun, the planets, and the moon.
Galileo was born
in Pisa, Italy, on February 15, 1564. Did
you know Galileo was born in the same year
as William Shakespeare? It is also the same year in
which Michelangelo died.
When Galileo was
born, Italy was not called Italy. Instead, Italy was
made up of independent city-states. The city-states
were in regions controlled by powerful families. Pisa
was located in the Tuscany region and controlled by
the Medici family.
Galileo's father was named Vincenzio,
and his mother was named Giulia. Vincenzio was a gifted
musician and mathematician, and he was also a cloth
merchant to earn extra money. Galileo was educated by
his father until he was 10 years old.
In 1574, Galileo's family moved
to Florence. The next year, Galileo attended the Benedictine
Monastery of Santa Maria di Vallombrosa, and he studied
Latin, Greek, music, logic, and religion. Galileo's
education prepared him to study at a university.
Earth Revolves Around the Sun
Before Galileo, people believed the earth was the center
of the universe and the sun revolved around the earth.
This theory is known as the Ptolemaic theory. It is
named after the Roman astronomer Ptolemy. The Greek
philosopher Aristotle and the Roman Catholic Church
also believed the sun revolved around the earth.
In 1543, Nicolaus Copernicus
published a new theory stating the earth revolves around
the sun. This is known as the Copernican theory. This
theory was considered a serious challenge to the Ptolemaic
theory and the Roman Catholic Church. Copernicus died
before he could prove his theory.
Moons of Jupiter
Galileo studied the Copernican theory and set out to
prove or disprove it. He did this by observing the universe
through the telescope.
In 1610, Galileo made an important
discovery about the planet Jupiter. He noticed there
were four "stars" near Jupiter. Galileo then realized
these "stars" were revolving around Jupiter. These "stars"
were really moons. This
observation helped prove the Copernican theory that
the earth revolves around the sun.
People knew the moon revolved
around the earth. They thought if the moon revolved
around the earth, then the sun must also revolve around
the earth. However, Galileo's discovery of four moons
revolving around Jupiter proved one object in space
can revolve around a second object in space while the
second object revolves around a third object in space.
To put it in a more simple way, it proved the moon can
revolve around the earth while the earth revolves around
After Copernicus and Galileo,
we know the earth revolves around the sun.
As you know, Galileo discovered
four of the moons of Jupiter. Did
you know Jupiter's other moons have been
discovered by observations from Earth and by the spacecraft
Voyager? In May, 2002, astronomers observed eleven new
moons around Jupiter. This made Jupiter the planet with
the highest number of known moons in our solar system.
Until the May, 2002, discovery, Saturn held the record
for the most known moons with 30. In February, 2003,
seven more moons were discovered around Jupiter. In
March, 2003, four more moons were discovered around
Jupiter. As of April, 2003, Jupiter has 60 known moons.
Keep checking back because the number of moons could
The four moons discovered by
Galileo are Jupiter's largest moons. They are Io, Europa,
Ganymede, and Callisto. Today, these moons are named
after Galileo and are known as the Galilean moons.
Jupiter is the largest planet
in our solar system. Our solar system is in the The
Milky Way galaxy.
In December, 1609, Galileo looked
at the earth's moon through the telescope, and he observed
many things regarding the moon that could not have been
known by looking at the moon with the human eye.
First, the moon does not create
light itself. The moon shines because it reflects light
from the sun.
Second, the moon's surface is
not smooth and perfect as Aristotle had believed. It
has mountains, craters, and valleys just like the earth.
In 1637, Galileo also discovered
the moon has a regular libration. A libration is a rocking
movement. This means a person can always see more than
half of the moon's surface.
Galileo made other important observations of the universe
with the telescope. He discovered:
Milky Way is made up of billions of stars
has phases similar to the moon
has "ears" which are the rings of Saturn
move across the surface of the sun
These observations by Galileo
led to the development of astronomy as a major branch
of science. Astronomy is the study of stars and planets.
Father of Modern Science
Galileo is known as the Father of Modern Science. He
was one of the first people to use the scientific method
to conduct experiments. This means Galileo observed
a situation, developed a theory, and then carried out
experiments to test his theory.
The idea of testing and experimenting
to prove or disprove a theory was revolutionary during
Galileo's time. Galileo used the scientific method to
disprove some of the beliefs of ancient Greek philosophers,
Laws of the Pendulum and Falling Bodies
Galileo began experimenting with pendulums after he
saw a chandelier swinging in the Pisa Cathedral. He
noticed each swing of the chandelier took the same amount
of time, even though each swing was shorter than the
previous swing. This led to Galileo's discovery of the
Law of the Pendulum.
Galileo also conducted experiments
with falling objects. Aristotle believed heavier objects
fall to the ground faster than lighter objects. As legend
has it, Galileo dropped two objects from the Leaning
Tower of Pisa to prove or disprove Aristotle's theory.
These objects were the same size, but different weights.
They fell to the ground at the same speed. This disproved
Aristotle's theory and led Galileo to discover the Law
of Falling Bodies.
Galileo died on January 8, 1642, in Arcetri, near Florence,
Italy. He was 77 years old. He is buried in the Santa
Croce cemetery in Florence.
Galileo's observations of the
planet Jupiter were very important. To honor his contributions,
the four moons of Jupiter which Galileo discovered are
called the Galilean Moons. These are Jupiter's largest
There is also a spacecraft named
after Galileo. It was launched on October 18, 1989,
to orbit Jupiter. It went into orbit around Jupiter
Galileo proved the earth revolved
around the sun. He was a great astronomer and scientist,
and he is a hero in our hearts.