telescopes space and technology

Extended Vocabulary concave convex infrared light pulsar quasar refl ecting telescope refracting telescope Vocabulary black hole constellation galaxy light-year nebula supernova Picture

Scott Foresman Science 5.16

Genre Comprehension Skill Text Features Science Content

• Captions

• Diagrams

• Glossary

Stars and Galaxies

ISBN 0-328-13963-7

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Scott Foresman Science 5.16

Genre Comprehension Skill Text Features Science Content

• Captions

• Diagrams

• Glossary

Stars and Galaxies

ISBN 0-328-13963-7

ì<(sk$m)=bdjgdh< +^-Ä-U-Ä-U

1 Explain the different ways in which convex

and concave lenses bend light

2 What is the advantage of the radio telescope?

3 What is a planisphere? How can it help

amateur astronomers?

discoveries using his refracting telescope

Write to explain the signifi cance of his discoveries Include details from the book

to support your answer

after the Hubble telescope was launched into space Summarize the problem and how it was solved

What did you learn?

Extended Vocabulary

concave convex infrared light pulsar

quasar refl ecting telescope refracting telescope

Vocabulary

black hole

constellation

galaxy

light-year

nebula

supernova

Picture Credits

Every effort has been made to secure permission and provide appropriate credit for photographic material

The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: Human Space Flight/NASA; 1 Science Museum, London /DK Images; 2 Human Space Flight/NASA; 3

©Anglo-Australian Observatory/DK Images; 5 Robin Scagell/©Galaxy Picture Library; 9 (T) Damian Peach/©Galaxy Picture

Library; 10 (TR) Science Museum, London /DK Images; 11 (TL) NASA; 12 Charles Walker / Topfoto /The Image Works,

Inc.; 13 John and Lisa Merrill/Corbis; 14 ©Roger Ressmeyer/Corbis; 15 ©Roger Ressmeyer/Corbis; 16 Human Space

Flight/NASA; 18 (B) Lester Lefkowitz/Corbis; 19 (TR) NRAO/AUI/©Galaxy Picture Library; 21 (TR) Bob Garner/©Galaxy

Picture Library; 23 NASA.

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson

ISBN: 0-328-13963-7

Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America

This publication is protected by Copyright, and permission should be obtained from the publisher prior to any

prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,

mechanical, photocopying, recording, or likewise For information regarding permission(s), write to

Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Barbara Fierman

For centuries people have been interested in events seen in

the sky They invented tools such as the astrolabe, the sextant,

and the telescope, and they built observatories to help them

explore the universe

Early astronomers, such as Galileo and Newton, used simple

telescopes These used mirrors and glass to make the stars appear

closer Telescopes used today are much bigger and more powerful

than early ones Radio telescopes have bowl-shaped dishes that pick

up radio waves given off by distant objects in space Space

telescopes, such as the Hubble, are launched into space beyond

Earth’s atmosphere, where viewing conditions are dark and clear

Our Sun is a star It is the closest star to Earth A star is a giant

ball of very hot gases that gives off heat and light energy A star’s

size, temperature, and distance from Earth affect how bright a star

looks to us, and its color tells us how hot it is

Hubble Space Telescope

2

What You Already Know

Telescopes have allowed scientists to measure a star’s distance from Earth in light-years A light-year is the distance light travels in one year, which is more than 9 trillion kilometers Telescopes have also allowed scientists to observe the birth and death of stars New stars form in a cloud of gas and dust called a nebula When some stars are at the end of their lives, they make a gigantic explosion called a supernova After this, stars sometimes become black holes, or points

in space with so much gravity that not even light can escape them

The Sun, Earth, and the other planets in the solar system are part

of a galaxy, or a huge system of stars, gases, and other material held together by gravity Scientists divide the galaxy into eighty-eight areas called constellations

Since their invention about four hundred years ago, telescopes have helped scientists learn many new things about the night sky Now let’s learn more about telescopes

3

This supernova was observed through a telescope.

Look Up

For thousands of years, people have been fascinated by the

night sky Ancient peoples built observatories where they plotted

the movements of the stars and planets Since then, astronomers,

or scientists trained to study space, have explored the stars and

planets to learn more about our galaxy and beyond The

invention of the telescope in the 1600s greatly improved

astronomers’ ability to study space

A telescope is an instrument that allows a viewer to observe

distant objects Since a telescope magnifi es objects, viewers can

observe, study, and take photographs of distant features in

the night sky Early telescopes used glass

lenses or mirrors to collect and

change light and focus images

This viewer uses a telescope mounted on a tripod to view and study objects in space.

5

The fi rst telescope was invented in the 1600s It consisted of

a long tube with a glass lens that gathered light at one end and an eyepiece that magnifi ed the image at the other end This is called a refracting telescope

It allowed people to see farther into space than ever before

But there were many more technological advances to come

An improvement on the refracting telescope was the refl ecting telescope This type of telescope used a curved mirror instead

of a glass lens It is easier to build large refl ecting telescopes than large refracting telescopes

After World War II, a new type of telescope was developed

The radio telescope picked up radio waves given off by stars, planets, and other objects in space By 1990 technology made

it possible to launch telescopes out into space This allows telescopes to deliver much clearer images because the light from distant objects does not pass through Earth’s atmosphere before entering the telescope When light passes through the atmosphere, some of it gets blocked This makes objects in space harder to see

Today, many types of telescopes are available They come in different sizes, ranging from small telescopes used by viewers

in their backyards to huge telescopes housed in observatories or orbiting Earth

Telescopes allow us to see the stars and planets with more detail Without a telescope, they look just like tiny points of light

Telescope Science

Telescopes work by bending light Some telescopes do

this with lenses Light bends when it enters the glass of a lens

This is called refraction Different types of lenses use refraction

to either focus or spread out light Convex lenses are thicker in

the middle than at the edges, and their surfaces are curved like

domes A wide beam of light entering a convex lens will be

focused to a very small point

Concave lenses are thicker at their edges than in their middles

Their surfaces curve inward, like bowls They spread narrow

beams of light into wider beams

A convex lens is thicker

in the middle than at the edge This type of lens focuses light.

A concave lens is thinner

in the middle and thicker

at the edge A concave lens spreads out light rays

6

Mirrors can also be used to focus or spread out light They do this by refl ecting light instead of bending it Convex mirrors have

a dome-shaped surface that spreads light Picture dropping

a rubber ball on an upside-down bowl The ball would bounce outward, away from the bowl’s center This is what happens to each ray of light that strikes a convex mirror

Concave mirrors have a surface that curves inward They focus light Picture dropping a rubber ball into a bowl that is sitting right-side up The ball would bounce inward, toward the bowl’s center This is how a concave mirror focuses light rays

Convex mirrors refl ect light in all different directions, spreading

it out

Concave mirrors refl ect light rays

in toward their center, focusing them to a point.

7

Refracting Telescopes

Refracting telescopes use lenses to

make images appear larger They consist

of a tube with a lens at each end The

fi rst lens, called the objective lens,

gathers and focuses light The viewer

looks through the second lens, called

the eyepiece lens It magnifi es the image

The fi rst refracting telescope was

invented by a Dutch eyeglass maker in

1608 Soon after, the great astronomer

Galileo Galilei built a telescope that

could magnify images to twenty times

their actual size One problem with

Galileo’s refracting telescope was that

the colors of objects would appear a little

off Another problem was that images

were blurred or fuzzy These problems

were reduced by using wide, thin lenses

But the wider a lens is, the longer a

telescope has to be to make it focus

properly Also, very large lenses are very

heavy If a lens is too large, it will start to

bend under its own weight, which changes

the shape of images

8

eyepiece lens magnifi es the image viewer

This diagram shows the path of light through a refracting telescope.

Modern refracting telescopes are far more powerful than Galileo’s telescope.

Galileo was the fi rst person to use a telescope to study the night sky Between 1610 and 1619, he made several important discoveries Galileo discovered that the Milky Way galaxy was made up of many stars, and that each star was at a different distance from Earth When he observed the Sun, he saw many spots on it When viewing the Moon, he noticed mountains and craters At that time, people believed that the Moon was a perfectly smooth ball, and Galileo proved that it wasn’t

Galileo observed four moons orbiting the planet Jupiter He also discovered that the planets Mercury and Venus revolve around the Sun At that time, people believed that Earth was the center of the universe Galileo’s discoveries led to his conclusion that the Sun was actually the center of the solar system His idea was not accepted for many years

In 1613 Galileo became the fi rst astronomer to spot the planet Neptune, which he thought was a star It wasn’t until 1846, more than two hundred years later, that scientists realized that Neptune was a planet Galileo’s many important discoveries led

to the building of better and more powerful telescopes

9

In 1610 Galileo discovered the phases of Venus with his telescope Its phases are similar to the Moon’s.

Objective lens collects light.

Phases of Venus

light

Refl ecting Telescopes

An English scientist, Sir Isaac

Newton, discovered that the lenses

of refracting telescopes split light into

different colors This made images

blurry Newton’s solution to the

problem was to use mirrors instead of

lenses Mirrors do not split light The

result of his work was the invention of

the refl ecting telescope

Newton’s refl ecting telescope had

a concave mirror at one end of a tube

and a fl at, tilted mirror in the center,

near the other end Light entered one

end of the telescope and traveled to the

other end, where it struck the concave

mirror This mirror gathered the light

and focused it on the fl at, tilted mirror

The tilted mirror refl ected light out

through a hole in the side of the tube

and into an eyepiece

10

large concave mirror

Refl ecting telescopes have

a large concave mirror that collects and concentrates light A second mirror refl ects the light to the user’s eye.

Newton invented the

fi rst refl ecting telescope

Newton’s telescope had several advantages over the refracting telescopes in use at the time Mirrors were much easier to make than lenses A lens must be made of very high quality glass with

no bubbles in it Also, a lens has two surfaces that must be perfectly shaped to give a clear image A mirror has only one surface to shape and polish

Newton’s telescope was also very powerful for its size This was an advantage because large refracting telescopes did not work very well To make a refracting telescope more powerful, the lenses had to

be moved farther apart Telescopes were built longer and longer, until some reached over forty meters! With such long

telescopes it was almost impossible to keep the lenses lined up correctly Refl ecting telescopes did not have this problem

11

plane mirror

Uranus

William Herschel built refl ecting telescopes using Newton’s design

Using a twelve-meter-long refl ecting telescope, he discovered Uranus in 1781 Later he discovered two of its moons.

Uranus

light

In ancient times, astronomers wanted dry, warm places to sit

while they observed the night sky The ancient Greeks and

Babylonians built simple buildings for viewing the stars These

buildings were the fi rst observatories In more recent times,

observatories have been built far from cities These locations are

very dark, making it easier to see the faint light of distant stars

Some observatories are built on high mountaintops When

telescopes are built in higher locations, light travels through less

of the atmosphere before reaching them This allows more light

to get to the telescopes

In the 1600s observatories were built to house refracting

telescopes The Paris Observatory, in Meudon, France, opened in

1670 In 1675 the King of England set up the Royal Greenwich

Observatory in Greenwich, England There, astronomers created

star charts to help sailors navigate on the seas

In the 1800s other types

of equipment, such as cameras, became important tools in observatories By the end of the 1800s, huge refracting telescopes were being built Special buildings with domes on top were built

to house these telescopes

12

This early observatory was built in India in

1726 It enabled early astronomers to study the sky with the naked eye

The Mauna Kea observatory is located on the island of Hawaii It is the largest observatory located on a mountain’s summit in the world Mauna Kea contains thirteen telescopes, which include both optical and radio telescopes Two of the largest optical telescopes in the world, Keck I and Keck II, are located in the observatory at Mauna Kea Astronomers from eleven different countries operate the telescopes

Mauna Kea is actually an inactive volcano on the largest

of the Hawaiian Islands It is the highest island mountain in the world, rising 4,205 meters above sea level The atmosphere above Mauna Kea is very dry and free of clouds As a result, there are more clear nights there than almost anywhere else in the world

Since its location is far from cities, there are no lights to interfere with the telescopes’ view The dark skies allow astronomers to view dim galaxies that lie at the edge of the universe

13

Mauna Kea observatory

in Hawaii is built on top

of a very tall mountain

Its height and clear weather provide an excellent view of the sky

Telescopes Today

If more light reaches a telescope, the image will be brighter

Bigger telescopes let in more light, so bigger telescopes are better

Until the end of the 1800s, very large telescopes had been

refracting telescopes The problems of earlier refracting telescopes

had been corrected by using complicated systems of lenses But

there was a limit to how large a lens could be made Since

high-quality mirrors could be made larger than lenses could, refl ecting

telescopes became the preferred choice

The Keck telescopes in the Mauna Kea observatory in Hawaii

are some of the largest refl ecting telescopes in the world Each

of the Keck mirrors consists of thirty-six smaller mirrors All

together, they make up a single mirror 10 meters across This

is called a segmented mirror Why not just build one large

mirror? Small mirrors are easier to make than large ones They are

also lighter, so they don’t bend under their own weight and don’t

change the images

14

The Keck telescopes in Hawaii

each contain a ten-meter-wide

mirror made up of thirty-six

smaller mirrors

The two Keck telescopes are located 85 meters from each other Using a special computer system, images from the two telescopes can be combined This allows the two 10-meter mirrors to act as one 85-meter mirror

An even more powerful system of telescopes is the VLT, which stands for “very large telescope.” It is located in Atacama, Chile The VLT is a set of four telescopes with mirrors about 8 meters across Working together with a computer system, these telescopes are as powerful as a single telescope with a mirror 200 meters across! The VLT produces clear images and is able to record light from even very faint and remote objects in the universe

15

This photograph shows just one segment of the Keck telescope mirror.

Astronomers realized that the layers of gases in Earth’s

atmosphere prevented them from observing dim objects The

gases of the atmosphere block some of the very faint light coming

from space In the 1970s scientists began to design a space-based

telescope that would observe space from outside of Earth’s

atmosphere In 1990 the Hubble Space Telescope was launched

into orbit

The Hubble is about the size of a school bus and weighs about

11 tons It is a refl ecting telescope made up of a system of mirrors

that refl ect light into several cameras and instruments The

primary mirror, shaped like a bowl, is 2.4 meters across and

weighs about 826 kilograms

The Hubble orbits about 600 kilometers above Earth It

provides images of objects that are billions of light-years away

The images received are converted into electrical signals and sent

by radio to the Hubble’s control center in the United States

Computers and radio equipment turn these signals into data

scientists can study

16

The Hubble Space

Telescope captures very

clear images of space

In spite of careful planning, the fi rst images sent by the Hubble were fuzzy

Scientists discovered that the primary mirror was not exactly the right shape It was off by just about two-thousandths of a millimeter

That tiny error was enough to make the images hazy So in December 1993, the space shuttle Endeavor was sent up

to repair the mirror It took astronauts fi ve tries over eleven days to fi x the telescope The mission was successful, and the images sent back from the Hubble were fi nally clear

Since it was launched into space, the Hubble has made several important accomplishments The telescope captured a better view of Mars than had ever been seen from Earth

Images from the telescope have proven that black holes really exist They confi rmed the existence of quasars, which are strange, distant objects that give off huge amounts of energy They have also given scientists a much better idea of how stars and galaxies are born and die

The Hubble has photographed several nebulae, or clouds of gas and dust, such as the Hourglass Nebula shown here The telescope was also able to get an outstanding view of the collision between the planet Jupiter and a giant comet

17

The Hourglass Nebula is a giant cloud made by a dying star as it spread into space The eye is the star’s collapsed core This image

of the Hourglass Nebula was captured by the Hubble telescope.

Hourglass Nebula