Britannica Student Encyclopedia - 2010

The northern slopes of the Urals are

mostly covered with forests. Common

trees include oak, linden, elm, fir, pine,

and spruce. Treeless land called tundra is

found in the far north, especially at high

elevations. Arctic foxes, reindeer, brown

bears, lynx, wolverines, and elk are

among the animals of the range.

The economy of the Urals depends on

mineral supplies. Mountain mines produce

iron ore, copper, chromite, gold,

silver, and platinum. Factories make

metal goods, chemicals, and machinery.

The huge forests of the Urals provide

valuable wood. Farmers in the south

grow wheat, buckwheat, millet, potatoes,

and vegetables.

Russians entered the northern Urals in

the late 1000s. However, they did not

discover the range’s mineral riches until

the 1600s. In the 1700s the Urals

became one of Russia’s most important

industrial areas.

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Russia

Uranus

Uranus was the first planet to be discovered

after the invention of the telescope.

It is the seventh planet from the sun. It

travels around the sun at an average dis-

The Belaya River runs through the southern

part of Russia’s Ural Mountains.

38 Ural Mountains BRITANNICA STUDENT ENCYCLOPEDIA

 

tance of about 1.8 billion miles (2.9

billion kilometers).

Physical Features

Uranus is the third largest planet in the

solar system. Its diameter, or distance

through its center, is about 32,000 miles

(51,000 kilometers). That is about four

times the diameter of Earth. Uranus is

most similar in size to Neptune, its outer

neighbor.

Uranus is one of the planets that are

called gas giants. It is made up mostly of

gases, mainly hydrogen and helium.

Small amounts of the gas methane give

the planet a blue-green color. Uranus has

no solid surface. Underneath its huge

layers of gases, it has a smaller area of

thick, hot liquid.

Narrow rings surround Uranus. These

rings seem very unlike the bright, icy

rings of the planet Saturn. The rings that

surround Uranus are made of some

unusually dark material.

Orbit and Spin

Like all planets, Uranus has two types of

motion: orbit and spin. Uranus orbits,

or travels around, the sun. It takes about

84 Earth years to complete one orbit. In

other words, a year on Uranus equals

about 84 Earth years.

Uranus spins about its center in an

unusual way. It is tilted so that it spins

nearly on its side. Also, Uranus is one of

the few planets in the solar system to

spin in a clockwise direction. Uranus

completes one rotation in about 17

hours, so a day on Uranus lasts about 17

hours.

Moons

More than 25 moons orbit Uranus. Its

five major moons are Oberon, Titania,

Ariel, Umbriel, and Miranda. They seem

to be composed of ice and rock. Some of

them have deep valleys and many large

pits called craters.

Observation and Exploration

Uranus cannot be seen from Earth without

the use of a telescope. The astronomer

William Herschel discovered

Uranus using his telescope in 1781. Uranus’

rings were discovered in 1977.

Only one spacecraft has visited the distant

planet. The unmanned U.S. spacecraft

Voyager 2 flew by Uranus in 1986.

#More to explore

Neptune • Planets • Solar System

• Space Exploration • Telescope

The spacecraft Voyager 2 photographed the

gassy planet Uranus in 1986. Experts

changed the colors in the image in order to

make the details easier to see.

Sometimes

storms occur

on Uranus.

However,

Uranus seems

to have fewer

storms than

the other gas

giants do.

BRITANNICA STUDENT ENCYCLOPEDIA Uranus 39

 

Urinary System

Humans need vitamins, minerals, and

other parts of foods and drinks in order

to live. As the body uses these things, it

creates substances that are not needed.

To stay healthy, the body must get rid

of these substances, called waste. The

digestive system forms solid waste from

food. Solid waste leaves the body

through the anus, at the end of the

large intestine. The urinary system

forms liquid waste, or urine, in the

kidneys. The bladder stores this urine

until it leaves the body through a tube

called the urethra.

Kidneys

In human beings and most other animals

the blood absorbs the wastes created

by the body. The blood carries these

wastes into two bean-shaped organs

called kidneys. The kidneys sit behind

the stomach on each side of the spine.

Kidneys do several things. They take

out any useful substances from the

blood and return them to the

bloodstream. They also take out liquid

wastes and extra water from the blood.

The kidneys then combine the wastes

and the water to make urine.

Bladder

Urine travels from each kidney down a

tube called a ureter. The two ureters lead

to the bladder. The bladder is a muscular

organ that expands like a balloon as

it fills with urine.

Urination

When the bladder is full, nerve endings

in the bladder send a message to the

brain. This message lets the person know

that the bladder needs to be emptied.

Blood containing waste enters a kidney. Within the kidney, tiny units called nephrons create

urine from waste and water in the blood. The blood then exits the kidney without the

waste. The urine leaves the kidney through a tube called the ureter.

40 Urinary System BRITANNICA STUDENT ENCYCLOPEDIA

 

Humans learn as children how to hold