receives only a little sunlight. Scientists
believe that the average temperature on
its surface is about .387° F (.233° C).
Orbit and Spin
Like the planets, Pluto has two types of
motion: orbit and spin. Pluto completes
one orbit around the sun every 248
Earth years. That means that a year on
Pluto lasts 248 Earth years. Pluto spins
about its center slowly. It completes one
rotation in about 6.5 Earth days, so a
Pluto day lasts about 6.5 Earth days.
Pluto is very difficult to photograph clearly
because it is so small and so far away.
BRITANNICA STUDENT ENCYCLOPEDIA Pluto 101
Pluto is tilted so that it spins nearly on
its side.
Moons
Pluto has three known moons: Charon,
Nix, and Hydra. Pluto and Charon are
closer in size than any of the planets and
their moons.
Observation and Exploration
In 1930 U.S. astronomer Clyde Tombaugh
discovered Pluto with the use of a
telescope. Scientists believed that Pluto
was the ninth planet in the solar system.
In 2006 the United States launched a
spacecraft, called New Horizons, to
explore Pluto. The journey to Pluto was
expected to take about nine years. Later
in 2006 scientists decided that Pluto
should be called a dwarf planet rather
than a planet. This brought the number
of planets down from nine to eight.
#More to explore
Neptune • Planets • Solar System
Pluto, god
#see Hades.
Plymouth
Colony
Plymouth Colony was the first lasting
English settlement in New England. It
was located on the site of the modernday
city of Plymouth, Massachusetts.
The city lies on Plymouth Bay, 37 miles
(60 kilometers) southeast of Boston.
Plymouth was founded by people called
Puritans. The Puritans were an English
religious group that practiced a strict
form of Protestant Christianity. They
disagreed with some practices of the
Church of England. Some Puritans were
called Separatists because they wanted to
separate themselves from the Church of
England. The Separatists who left
England and founded Plymouth are
now known as the Pilgrims.
The Pilgrims crossed the Atlantic Ocean
on a ship called the Mayflower. They
reached Cape Cod in November 1620.
It took them until December 21 to
decide where to settle. They named the
chosen site Plymouth because the Mayflower’s
voyage had started in Plymouth,
England. According to tradition, the
Pilgrims landed on Plymouth Rock on
December 26.
Winter had already set in when the Pilgrims
landed. They were short of food.
Many became ill. More than half the
Pilgrims did not survive the first winter.
The Pilgrims who did survive got help
Pluto is only
about twothirds
as large
as Earth’s
moon.
An old picture shows the landing of the Pilgrims
at Plymouth Rock.
102 Pluto, god BRITANNICA STUDENT ENCYCLOPEDIA
from Native Americans who lived
nearby. The Wampanoag people taught
the Pilgrims how to plant crops, fish,
and hunt.
Between 1630 and 1640 the Plymouth
colonists made a good living by trading
with the new Massachusetts Bay Colony.
In 1691 Plymouth Colony became a
part of the Massachusetts Bay Colony.
..More to explore
Colony • Massachusetts Bay Colony
• Mayflower • Puritans •Wampanoag
Pneumonia
Pneumonia is an inflammation, or swelling,
of tissue in the lungs. An infection
usually causes this inflammation. Pneumonia
makes breathing difficult and
even painful.
The main symptoms, or signs, of pneumonia
are coughing, fever, chest pain,
and shortness of breath. People with
pneumonia may also have headaches,
sweating, and confusion.
Pneumonia is not a single disease. Many
things, including bacteria, viruses, and
fungi, can infect the lungs and cause
pneumonia. The infection can spread to
others when the infected person coughs
or sneezes.
Substances called vaccines can prevent
some forms of pneumonia.Washing
one’s hands may also help to stop infections
that lead to pneumonia. In addition,
people should always cover their
mouth when sneezing or coughing.
Treatment for pneumonia includes taking
medicines that fight the infection
and getting plenty of rest. Some people
with pneumonia may need to go to a
hospital for drugs and extra oxygen.
With medical treatment, most people
recover from pneumonia within a few
weeks.
..More to explore
Cough • Lung • Vaccine
Pocahontas
Pocahontas may be the most famous
Native American in history. She helped
to make peace between Native Americans
and the English colonists of
Jamestown, Virginia.
Pocahontas was born in about 1595.
Her father, Powhatan, was a powerful
Indian leader. Pocahontas was about 12
years old when she first met the colonists.
The English leader John Smith
Doctors find pneumonia by looking at chest
X-rays. The lung at left is infected.
Viruses cause
about half of
all cases of
pneumonia.
BRITANNICA STUDENT ENCYCLOPEDIA Pocahontas 103
later claimed that young Pocahontas
saved his life. Smith said that Powhatan’s
men took him prisoner and were
going to kill him. But Pocahontas got
her father to free him.
The story has become part of American
folklore, but it may not be true. Smith
liked to tell tales. Nevertheless, Pocahontas
was helpful. She brought food to the
settlers as their supply ran low. She also
warned them of possible Indian attacks.
