Childrens Illustrated Encyclopedia

451

Mapping Earth

resources satellites take pictures of

Earth’s surface. the cameras have

various filters so they can pick up

infrared (heat) radiation and different

colors of light. Vegetation, for instance,

reflects infrared light strongly, showing

up forests and woodlands. Computer-

generated colors are used to pick

out areas with different kinds of

vegetation and minerals.

The planet Jupiter with two of its

natural satEllitEs moons, Io (left) and Europa (right)

the planets in the solar system

have 173 known natural satellites

(moons) altogether. Most of these

orbit (move around) the four

giant outer planets: Jupiter, saturn,

uranus, and neptune. the largest

moons are bigger than Mercury, the

smallest planet; the smallest moons

are only a few miles across and have

irregular, potatolike shapes.

Satellite map image

of San Francisco Bay,

California. Clearly visible

are two bridges: the

Golden Gate Bridge

on the left and the

Bay Bridge on

the right.

satEllitE orbits

some communications satellites take

one day to orbit Earth, so they appear

to remain fixed over one location. this kind

of orbit is called geostationary. a polar orbit

allows a satellite to see the whole Earth in a

series of strips. in an elliptical orbit, a satellite

can pass low over a selected part of Earth.

Geostationary orbit, used

by communications satellites

Elliptical orbit, used

by spy satellites

Solar panels

generate

electricity from

sunlight to power

the satellite.

artifiCial

satEllitEs

there are many types of

artificial satellites. Weather

satellites observe rain, storms,

and clouds, and measure land and

sea temperatures. Communications

satellites send radio and television

signals from one part of Earth to

another. spy satellites observe military

targets from low altitudes and send back

detailed pictures to ground stations.

Earth observation satellites monitor

vegetation, air and water pollution,

population changes, and geological

factors, such as mineral deposits.

Radar altimeter provides

data on wind speed, ocean

currents, and tides.

WhEn airCraft and

balloons first took to the skies, the people

in them were amazed at their new view

of the world. from hundreds of feet

up they could see the layout of a large

city, the shape of a coastline, or the patchwork

of fields on a farm. today, we have an even wider view.

satellites circle Earth, not hundreds of feet, but hundreds

of miles above the ground. from this great height, satellites

provide a unique image of our planet. some have cameras that take

photographs of land and sea, giving information about the changing

environment on Earth. others plot weather patterns or peer out into

space and send back data (information) about planets and stars. all

of these are artificial satellites that have been launched into space

from Earth. however, the word satellite actually means any object

that moves around another more massive one while being held in

orbit by gravity. there are countless natural satellites in the

universe: Earth has one—the moon.

Sputnik 1

on october 4, 1957, the

soviet union launched

the world’s first artificial

satellite, sputnik 1. it

carried a radio transmitter

that sent signals back to

Earth until sputnik 1

burned up in the

atmosphere 92 days later.

Polar orbit, used by Earth

observation satellites

Antenna for transmitting

data back to Earth

Find out more

astronomy

geology

navigation

space flight

telephones

television

Earth observation

satellite ERS-2

Infrared scanner

measures water vapor in

the atmosphere and the

temperatures of seas and

cloud tops.

SatelliteS

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