Because the Galapagos are so isolated,
the plants and animals found there are
very unusual. Cactus forests grow in the
dry lowlands, while the uplands are covered
with thick, moist vegetation, such
as ferns and mosses. Giant tortoises were
once so abundant that Spanish explorers
named the islands for them. The Spanish
word galapago means “tortoise.” The
islands also have rare marine iguanas.
The United States issued a postage stamp
100 years after the Gadsden Purchase. The
stamp honored the pioneers who settled on
the land that was purchased from Mexico.
80 Galapagos Islands BRITANNICA STUDENT ENCYCLOPEDIA
The Galapagos Islands belong to Ecuador,
and most of the people living there
are Ecuadorans. They live on the larger
islands. Many of the islands have no
people. The island of Baltra has a military
base. Tourism, fishing, and agriculture
are the main parts of the economy.
#More to explore
Darwin, Charles • Ecuador • Evolution
Galaxy
A galaxy is a group of stars, clouds of
gas, and dust particles that move
together through the universe. There are
billions of galaxies in the universe. They
probably formed billions of years ago,
soon after the universe began.
The sun, Earth, and the other planets of
the solar system are part of the Milky
Way galaxy. Most galaxies move through
the universe as part of clusters, or
groups, of galaxies. The MilkyWay is at
one end of a cluster called the Local
Group. It includes about 40 galaxies.
Size
Even the smaller galaxies are made up of
millions of stars. These galaxies may be
5,000 light-years across. (A light-year is
the distance light travels in a year—
about 5.8 trillion miles, or 9.5 trillion
kilometers.) The MilkyWay is roughly
20 times larger than that. It includes
hundreds of billions of stars. The largest
galaxies are even more huge and contain
trillions of stars.
Shape
Galaxies are divided into three main
categories based on their shape: spiral,
elliptical, and irregular. Spiral galaxies
look like pinwheels. They have a central
disk and two or more curved arms winding
outward. The disk consists mainly of
older stars, while the arms have younger
stars. The arms contain much dust and
gas, from which new stars can form. The
MilkyWay is a spiral galaxy.
An elliptical galaxy may be shaped like a
round ball or may be more stretched
out, like an American football. It has
more stars near its center and fewer stars
Isabela Island is the largest of the Galapagos
Islands. Giant tortoises can be found
there.
The Whirlpool Galaxy is a large spiral galaxy.
To the right is a smaller galaxy.
BRITANNICA STUDENT ENCYCLOPEDIA Galaxy 81
in its outer regions. Elliptical galaxies
vary widely in size. Small elliptical galaxies
are the most common kind of galaxy
in the universe.
Unusually shaped galaxies are called
irregular galaxies. They are not very
common. Many of them have no obvious
center point. Some of them appear
to be the result of a crash between several
galaxies.
#More to explore
MilkyWay • Star • Universe
Galileo
Galileo has been called the founder of
modern science. He was one of the first
people to examine the heavens with a
telescope. He also made breakthrough
discoveries in the study of motion.
Galileo Galilei, who is generally known
by his first name, was born in Pisa, Italy,
on February 15, 1564. He entered the
University of Pisa to study medicine but
later switched to mathematics.
EarlyWork
Galileo was interested in studying the
effect of forces on the motion of bodies.
In the Cathedral of Pisa he observed a
chandelier swaying back and forth. He
realized that it took the same time for
each swing, whether the swings were
large or small. This discovery became
known as the law of the pendulum. It
led to the use of the pendulum to keep
track of time.
Use of the Telescope
In about 1609 Galileo learned of the
invention of the telescope in the Netherlands.
He later built his own version.
The telescope allowed Galileo to make
discoveries about space. On January 7,
1610, he discovered four moons revolving
around the planet Jupiter. In his
honor, these bodies are known as the
Galilean satellites.
Discoveries Galileo made provided evidence
that the sun is the center of the
solar system. Nicolaus Copernicus,
another famous astronomer, had put
forth this theory in 1530.
Punishment and Death
Galileo’s studies brought him into conflict
with the Roman Catholic church.
The church still taught that Earth was
the center of the universe. Galileo was
ordered not to teach or defend the ideas
of Copernicus. He continued to do so,
however.
In 1633 Galileo was brought before the
Inquisition, a Roman Catholic institu-
Galileo tion that held power then. He was pun-
82 Galileo BRITANNICA STUDENT ENCYCLOPEDIA
ished by being told he could not leave
his house.
Galileo became blind in 1637 but continued
to work. He died on January 8,
1642.
#More to explore
Pendulum • Telescope
Gama, Vasco da
The Portuguese navigator Vasco da
Gama made three sea voyages to India
between 1497 and 1524. His voyages
opened a sea route fromWestern Europe
to the East and made Portugal a world
power.
Early Life
Little is known about Vasco da Gama’s
