Childrens Illustrated Encyclopedia

517

From Far away, a person looks like a tiny dot. But with a telescope, you can

see a clear, bright image that reveals all the details of that person’s face. Large

modern telescopes make it possible for astronomers to make images of

extremely faint objects in the universe, such as galaxies billions of light years

away, or small icy worlds at the edge of the solar system. Less powerful

telescopes are important too: they are valuable tools for mapmakers,

sailors, and bird watchers. Telescopes have helped scientists

make some of the greatest discoveries about the universe.

In 1609, the Italian scientist Galileo first turned a

telescope to the skies. His observations led him to

suggest that Earth moved around the sun and

was not the center of the universe, as people

believed at that time. Since then, astronomers

have continued to build ever bigger and

better telescopes and to make new and

unexpected discoveries with them.

The European Extremely Large Telescope (E-ELT), right,

will be the world’s largest telescope when it becomes

operational in 2024. It will not use lenses, like binoculars,

but a large primary mirror made up of smaller segments.

rEFLEcTInG TELEScopE

most astronomers use reflecting telescopes, the best

telescopes for picking up the faint light from distant stars.

a large curved mirror catches the light and concentrates

it to form an image. For observing directly by eye, a

smaller mirror then carries the image to a lens called

the eyepiece. In large telescopes used by professional

astronomers, the light goes into an electronic instrument

or camera, and the observations are stored in a computer.

The objective

lens is a convex

lens that concentrates

the light to form an image.

rEFracTInG TELEScopE

a large lens at the front of a refracting

telescope refracts, or bends, the light to

form an image of a distant object. The

eyepiece lens is at the back. Some

refractors have a third lens in the

middle. without this lens, the telescope

would produce an upside-down image.

Telescopes

Radio telescopes

Some galaxies and other objects in

space give out invisible radio waves

as well as light. astronomers study

the universe with radio telescopes,

which are large dish-shaped

antennas that pick up radio waves

from space. radio astronomy has

led to the discovery of dying stars

and distant galaxies

that would not

have been

seen from

their light

alone.

The primary mirror is made from 36

small hexagons that work like a single

mirror. Together, these segments

collect light and reflect it to focus

on the secondary mirror.

The middle

lens turns

the image

the right

way up.

Find out more

astronomy

Light

microscopes

Science, history of

opEra GLaSSES

opera glasses are the simplest

kind of binoculars. They consist

of two small telescopes placed

side by side.

BInocuLarS

Binoculars are more

complex than opera glasses.

They contain a system of

lenses and prisms that

makes them powerful yet

small in size.

The structure keeps all

parts in same relative

positons as telescope

turns and tilts.

Light enters the front

of the binoculars.

A prism is a

triangular-shaped

piece of glass.

Eyepiece lenses are

adjustable to match the

strength of each eye.

Prisms “fold up”

the light inside the

binoculars, which

magnifies objects

as much as a

long telescope.

The tertiary

mirror reflects

light to cameras

and scientific

instruments.

The eyepiece lens focuses

the image into the

observer’s eye.

The secondary

mirror bounces

light back down

adaptive mirror will make Computer-controlled to tertiary mirror.

the images as sharp as

those of a space telescope.

Cameras

and scientific

instruments.

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