100 Mental Illness BRITANNICA STUDENT ENCYCLOPEDIA
to think clearly, however, and may make
poor decisions.
Mental Disorders in Children
Some mental disorders can begin during
childhood or adolescence (the teenage
years). Attention-deficit/hyperactivity
disorder (ADHD) is the most common
one. Children with ADHD may have
trouble paying attention in class. They
may find it difficult to stay seated for
long. ADHD is more common in boys
than in girls.
Eating disorders—including anorexia
and bulimia—are serious mental illnesses
that usually start during adolescence.
People with eating disorders,
usually girls, have a strong fear of gaining
weight. They often think they are fat
when they are really thin. People with
anorexia eat very little food. People with
bulimia eat a lot of food and then make
themselves throw up. Eating disorders
can cause physical problems and even
death.
Causes
Mental illness may be caused by
chemical problems in the brain,
genetics, environmental factors, or a
combination of these things. For
example, chemical problems in the
brain may cause mood disorders or
schizophrenia. Genetics may also be
responsible, however: children whose
parents have schizophrenia or
depression are more likely to have those
disorders. Environmental factors—such
as child abuse or extreme stress—may
add to the likelihood of mental illness.
For many mental illnesses, the exact
causes are unknown.
Treatment
Psychiatrists are medical doctors who
treat the mentally ill. Psychiatrists may
prescribe medication to reduce the
symptoms of some mental disorders.
Some medications are very effective.
They allow patients to resume normal
lives.
Psychotherapy (often called simply
therapy) is another effective treatment
for many mental disorders. During
therapy, patients talk about their feelings
and behaviors with a therapist. Therapists
include psychiatrists, psychologists,
social workers, and counselors. Therapists
help people learn to control the
symptoms of their mental disorder.
Mercury
Mercury is one of the planets that orbit,
or travel around, the sun in the solar
system. It is the closest planet to the sun.
Children who survived a terrible storm in
Indonesia do art therapy. Art therapy can
help children to deal with stress. If not
treated, extreme stress can cause some
types of mental illness.
Austrian
doctor
Sigmund Freud
helped
develop “the
talking cure.”
Patients talk
about their
feelings and
actions with a
therapist.
BRITANNICA STUDENT ENCYCLOPEDIA Mercury 101
Its orbit, or path, is between the sun and
the orbit of the planet Venus. Mercury’s
average distance from the sun is about
36 million miles (58 million kilometers).
It travels around the sun at a faster
speed than any other planet.
Physical Features
Mercury is the smallest planet of the
solar system. It is less than half the size
of Earth. Mercury’s diameter, or
distance through its center, is about
3,000 miles (4,900 kilometers). It is a
solid, rocky planet. Mercury is very
heavy for its size. This is because it has
a huge core, or center, made of iron.
Mercury’s landscape includes flat plains
and long, steep cliffs. Its surface is
scarred by pits called craters. The
craters form when chunks of rock or
metal called meteorites hit Mercury.
Some parts of the surface have many
craters, while other parts are very
smooth.
A thin atmosphere, or layer of gases,
surrounds Mercury. It does not keep in
heat well. Mercury has daytime temperatures
of about 755° F (400° C).
However, the temperature may fall to
about .280° F (.173° C) before dawn.
Orbit and Spin
Like all planets, Mercury has two types
of motion: orbit and spin. Mercury
orbits, or travels around, the sun very
quickly. It orbits at an average rate of
about 30 miles (48 kilometers) per second.
Mercury completes one orbit
around the sun every 88 Earth days. In
other words, one year on Mercury lasts
88 Earth days.
On the other hand, Mercury spins very
slowly. The planet takes nearly 59 Earth
days to rotate once about its center.
This combination of a fast orbit and a
slow spin leads to an unusual situation.
A day on Mercury—the time it takes for
the sun to appear straight overhead, to
set, and then to rise straight overhead
again—lasts about 176 Earth days. So
on Mercury a “day” is longer than a
“year.”
Observation and Exploration
Mercury is so close to the sun that it is
difficult to see it well from Earth. Much
of the information known about Mercury
came from Mariner 10, the first
spacecraft to visit the planet. The
unmanned U.S. craft flew by Mercury
in the 1970s. The United States
A picture taken from a spacecraft
shows the cratered surface
of Mercury.
102 Mercury BRITANNICA STUDENT ENCYCLOPEDIA
launched a second unmanned craft,
called Messenger, to Mercury in 2004.
#More to explore
Meteor and Meteorite • Planets • Solar
System • Space Exploration • Sun
Mercury, god
#see Hermes.
Meredith, James
James Meredith was a leader of the civil
rights movement. In 1962 he became
the first African American student at the
University of Mississippi. His struggle to
enter the school made him famous
throughout the United States.
James Howard Meredith was born on
