Childrens Illustrated Encyclopedia

Buoy s

Floating

markers called

buoys mark dangers,

such as hidden rocks.

Buoys either mark a safe

channel or indicate the

dangerous areas themselves.

The shape and color of the buoys

show on which side a boat should pass.

AuTopiloT

The autopilot will

keep a boat or a

plane on a chosen course by

adjusting the steering gear

automatically. The autopilot of an

airliner controls the plane for most

of its flight. some computerized

autopilot systems can even guide a

plane through takeoff and landing.

A sonic depth

finder measures depth

of water, which is important

for navigating around coasts.

It beams high-pitched

sound waves towards

the sea bed. The time

taken for the echo

to return gives

the depth.

Radar warns a navigator of nearby objects

such as other boats or aircraft. A radar

scanner sends out a beam of radio

waves as it rotates, and receives

the echoes bouncing back

from any

object

within

range.

Boats and

airplanes use

signals beamed

from navigation

satellites, such as

those of the Global

Positioning System

(GPS), to guide

them anywhere in

the world.

For safety, a boat or

aircraft traveling at

night carries a red

light on the port side

(left) and a green

light on the

starboard side

(right). This tells

others the

direction it is

traveling in.

EvEn in A ciTy with signs and street names to help you, it is easy to get lost.

But imagine if you were out in open country or sailing in a boat without a map.

How would you find your way? The earliest sailors faced this problem as they

made their voyages of discovery. The answer was to watch the sun by day and

the stars by night. Because the sun always rises in the east and sets in the

west, sailors could work out in which direction they were traveling. The

position of stars in the sky also gave them their direction: polaris,

the north star, for instance, is almost in line with Earth’s north pole.

navigation is the process of working out where you are and in which

direction you are traveling. This can be on land, at sea, or in the air.

Today, navigators have many aids to help them

find their way. There are detailed maps of

almost every part of the world, and electronic

systems that use radar and satellites can fix

the position of an aircraft or ship to within

a few yards. such advances in navigation

make even the longest journey easy

and safe.

373

sExTAnT

For more than 250 years, navigators

have used a device called a sextant.

A sextant gives a measurement of

the angle between two objects, such

as the horizon and the sun. From

this angle, it is possible to work out

the latitude of a ship or aircraft.

A radio receiver on board

a boat compares the

times that signals arrive

from land-based

radio beacons and

uses this information

to calculate the

boat’s position. This

system is called

radio direction

finding.

Buoy with

radar reflector

Find out more

Aircraft

Magnetism

oceans and seas

ports and waterways

satellites

ships and boats

nAvigATion sysTEMs

Today, ships and aircraft routinely travel around

the world without any danger of becoming lost.

They are equipped with electronic systems that use

radio beacons on land and navigation satellites in

space. These systems calculate the location of a ship

or aircraft and the direction in which it is traveling

with great precision.

LiGHtHOUse

coastal waters can be

dangerous because

of rocks and tides.

lighthouses send out a

bright beam of light to

warn ships. The interval

at which the light flashes

identifies the lighthouse

and so helps navigators

find their position.

Navigation

MAp And

coMpAss

Marks on a map

show paths, hills, and

other features. A magnetic

compass shows which way to

point a map so that it represents

the landscape. The chinese first

used magnetic compasses about

1,000 years ago; about 2300 bce the

first map was drawn in Babylon.

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