Download Journey through the cosmos

Science
Stage 5
Journey through the cosmos
Set 1: Thinking BIG
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Photo credit: NASA
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Number: 43939
Title: The cosmos
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Photograph of spiral galaxy courtesy of NASA
Extract from Science Syllabus Years 7-10 © Board of Studies, NSW 2003
Photograph of Crab Nebula © Malin/Pasachoff/Caltech
Various photographs courtesy of NASA
Various photographs courtesy of NASA/JPL/Caltech
Photographs of two constellations © David Malin
Photograph of a radio telescope © Jane West
Photograph of the Anglo-Australian telescope © Anglo-Australian Observatory
Photograph of young stars © Anglo-Australian Observatory/Royal Observatory Edinburgh
Part covers, Set 1
p 8, Set 2 p 30
Introduction
Set 1 p 18
Set 1 p 8, Set 2 p 2,
Set 3 p 21,
Set 4 pp 7, 23, 24,
26, 28, 36
Set 2 pp 21, 23, 43.
Set 3 p 33, Set 4 p 3
Set 3 p 8
Set 3 p 10
Set 3 p 24
Set 3 p 32
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pursuant to Part VB of the Copyright Act 1968 (the Act).
The material in this communication may be subject to copyright under
the Act. Any further reproduction or communication of this material by
you may be the subject of copyright protection under the Act.
CLI Project Team acknowledgement:
Writer:
Editors:
Illustrator:
Jeanette Rothapfel
Rhonda Caddy and Jane West
Tom Brown and Rhonda Caddy
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.
Published by
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Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or
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© State of New South Wales, Department of Education and Training 2005.
i
Unit outline
Here are the names of the lessons in this unit.
☞
Set 1
Set 2
Set 3
Set 4
Thinking BIG
Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
Lesson 6
Some models of the Universe
Galaxies
Stars: the building blocks of galaxies
The life cycle of a star
Stellar colour, brightness and size
Cosmic distances
BIG questions
Lesson 7
Lesson 8
Lesson 9
Lesson 10
Lesson 11
Lesson 12
The evolution of the Universe
Models of the expanding Universe
Remains of the big bang
More evidence – redshift, blueshift
The case of the missing matter
Machos, wimps or …?
A BIG search
Lessons 13 and 14
Lesson 15
Lesson 16
Lesson 17
Lesson 18
Tools of the optical astronomer
More tools of an astronomer
Invisible astronomy
Australian astronomy
The BIG picture
A BIG dream
Lesson 19
Lesson 20
Lesson 21
Lesson 22
Lesson 23
Lesson 24
Anyone out there?
Other solar systems?
SETI in Australia
Chances of life elsewhere?
What might ET look like?
The search for life on Mars
Journey through the cosmos Set 1
ii
Set 1: Thinking BIG
Contents
What will you learn in Set 1? ...................................................................iii
What do you need for Set 1? ....................................................................iv
Lesson 1
Some models of the Universe .............................. 1
Lesson 2
Galaxies................................................................... 7
Lesson 3
Stars: the building blocks of galaxies ............... 11
Lesson 4
The life cycle of a star ......................................... 15
Lesson 5
Stellar colour, brightness and size .................... 25
Lesson 6
Cosmic distances ................................................. 31
Checking your progress........................................................................... 38
Suggested answers ................................................................................... 39
Send-in pages ............................................................................................ 45
Journey through the cosmos Set 1
iii
What will you learn in Set 1?
In Set 1, you will have opportunities to:
•
identify some of the people, and their ideas, that have contributed
to the current model of the Universe
•
outline the current model of the Universe
•
relate the time of life on Earth to the age of Earth and the age of
the Universe
•
identify refraction (bending) and dispersion (splitting into colours)
of sunlight as it travels through a ‘prism’
•
describe the life stages of a star
•
summarise the life cycle of a star
•
compare stars with different colours, brightnesses and sizes
•
compare some units used to measure distances in the Universe
•
extract information about the Universe and models of the Universe
from tables, text and diagrams
•
combine and organise information to write clear descriptions and
explanations about the Universe and models of the Universe.
Journey through the cosmos Set 1
iv
What do you need for Set 1?
Here is a reminder of the items you need for Set 1.
Lesson 3
•
beaker or a straight-sided glass
•
scissors
•
a piece of cardboard
•
white paper
Lesson 5
•
ruler
•
sharp pencil
•
scissors
•
sheets of newspaper
Lesson 6
•
calculator
•
piece of chalk
Journey through the cosmos Set 1
1
Lesson 1
Some models of the Universe
Have you ever stood and gazed up at the night sky? Amazing, isn't it!
Everything that exists, including you standing on Earth, is part of the cosmos.
From ancient times to the present, people have been fascinated by the cosmos,
or Universe, and have tried to explain its structure and how it works.
Their ideas may be called 'models'. A model can be as simple as an idea
or picture that attempts to explain observations made.
There have been many different models of the Universe throughout history.
Different cultures also have different models. In this lesson, you'll read
about some models that have lead to the current scientific model of
the Universe and complete some activities to help you understand these
models. Then you'll use the information to complete a send-in exercise.
Journey through the cosmos Set 1
2
Examples of ancient models of the Universe
Models described by the ancient Greeks placed Earth as
the supreme centre of the Universe. Aristotle (384–322 BC)
pictured the Universe with Earth at its centre. No one dared
question the teachings of such a famous man who was tutor
to Alexander the Great. This idea became law and continued
for centuries. However, Aristotle could not account for why
the planets moved at different speeds or that sometimes
they moved forward and then they moved backward.
Claudius Ptolemy (100–170 AD), Greek-born in Egypt,
attempted to explain these problems. He also described
an Earth-centred Universe* called a geocentric model.
But, he described the planets as moving in small circles
called epicycles as they moved in their major circular orbits.
Although not correct, Ptolemy's model accounted for
the strange forward and backward motion of the planets.
Sun
Earth
Moon
Mercury
Nicolaus Copernicus (1473–1543) was a Polish astronomer
who introduced into astronomy the most far-reaching changes
since ancient times. He suggested that the Sun was at the centre
of the Universe* and not Earth. Such a sun-centred model
is called a heliocentric model. Copernicus was not the first person
to suggest such a model. Aristarchus, 260 years BC,
also made this claim but his idea was unsupported.
*
Remember that astronomers who lived in these times did not realise
that the Sun and the planets were part of a smaller system now called
the Solar System.
Journey through the cosmos Set 1
3
Has the model of Copernicus changed?
Here is a diagram of the Sun-centred model of Copernicus.
The stars
Sun
Earth’s orbit
off centre
Saturn
Sun
Venus
Jupiter
Mercury
Mars
The model of Copernicus is not the one we use today because
we now realise that:
•
the planets move in elliptical orbits around the Sun
and not in perfect circular orbits. This was a discovery by
Johannes Kepler (1571–1630) as a result of mathematical
calculations using data from accurate night sky observations
made by Tycho Brahe (1546–1601).
Kepler also developed laws that state how:
–
planets move faster in their orbit the closer they get to the Sun
–
planets take a much longer time to orbit the Sun the further
they are from the Sun.
•
the planets appear to move forward and backward because
the planets move at different speeds in their orbits.
This to and fro motion is only an illusion. When Mars is
observed from Earth, it may first appear to be in front of Earth.
But, because Earth is travelling much faster in its orbit,
Earth can overtake Mars which falls behind Earth.
This gives the appearance that Mars has moved backwards.
Astronomers call this apparent movement 'retrograde motion'.
Journey through the cosmos Set 1
4
What is an ellipse?
An ellipse is oval in shape. Elliptical means shaped like an ellipse.
Galileo and Newton
Galileo Galilee (1565–1642), the famous Italian scientist,
made significant contributions to astronomy. Although he did not
invent the telescope, Galileo was the first to use a telescope
to observe the sky. Among his discoveries, he found four moons
moving around Jupiter so demonstrating that Earth was not
the centre of all things as Aristotle and Ptolemy claimed.
He was convinced that Earth moved around the Sun but
he was arrested for promoting the model of Copernicus and,
under the threat of death, retracted his ideas and spent
the rest of his life confined to his home under house arrest.
Sir Isaac Newton (1642–1727), a brilliant English mathematician,
rebuilt the model described by Copernicus by using the new ideas
of force and gravity. Each planet was locked into its elliptical orbit
by gravity. He regarded Earth as just another planet,
third from the Sun, in a Universe of stars much more distant
than Earth is from the Sun. His well known laws of motion
and the law of universal gravitation not only applied to objects
on Earth but to everything in the heavens.
What is the contemporary model
of the Universe?
The contemporary model of the Universe has been improved
by knowledge that:
•
the Sun and planets form the Solar System
•
the Solar System is one insignificant, small part of a galaxy
called the Milky Way
•
the Milky Way is one of billions of galaxies in the Universe.
And who knows? Our Universe might be only one of many
Universes that scientists have yet to discover!
Journey through the cosmos Set 1
5
So, as you can see, our model of the Universe today varies greatly
from ancient Greek times. Contemporary models are based on
careful observations, debate, mathematics and physics (the study of
the behaviour of matter and energy). But, it has only been in
very recent scientific history that we have had the tools to test
our models of the Universe. You'll learn more about these tools
throughout this unit about the past, present and future of the cosmos.
Time and the Universe
Here is an activity to give you a better understanding of the age of
our Universe.
The items in the column on the left below are major events (from
our 'Earthling' perspective) in the history of the Universe.
They are in order from oldest to most recent down the column.
Draw a line to match each event with a time in the column on the right.
(Don’t be tricked! A billion is a million million.)
Event in the Universe
Approximate time of the event
1.
origin of the Universe
(called the big bang)
13 billion years ago
2.
formation of galaxies
3.5 million years ago
3.
formation of our Solar System
(our Sun and planets)
4.
first life on Earth
65 million years ago
5.
extinction of the dinosaurs
4.5 billion years ago
6.
appearance of human ancestors
15 billion years ago
4 billion years ago
Check your answers now.
Exercises 1.1 and 1.2
Use information from Lesson 1 to complete these send-in exercises.
Journey through the cosmos Set 1
6
Journey through the cosmos Set 1
7
Lesson 2
Galaxies
What do you see when you look out into the night sky? If the night
is dark and cloudless, you will see twinkling stars everywhere.
But some of the ‘stars’ you see are really huge groups of stars
called galaxies.
What is a galaxy?
The stars in the Universe are grouped together in very large spinning
structures called galaxies. A galaxy contain millions and even
billions of stars along with clouds of gas and dust called nebulas,
and planets, all held together by gravitational forces.
Even though galaxies are the largest objects in the Universe,
you will only see them as pinpoints of light because they are
so very far away.
The only galaxies that are easily visible with the naked eye
from Earth are the fuzzy, cloud-like formations of
the Large and Small Magellanic Clouds. These are
the closest galaxies to our own galaxy, the Milky Way.
The Milky Way is a good name for our galaxy because the word galaxy
comes from the Greek word for milk, gala.
Journey through the cosmos Set 1
8
What are the different kinds of galaxies?
There are three main ways to classify galaxies.
Spiral galaxies have two or more ‘arms’ and look like a UFO or
fried egg when viewed from the side. A spiral is a flattened disc
with a number of arms and a bulge of stars at the centre.
A very well-known spiral is the Whirlpool.
Photo credit: NASA
•
A spiral galaxy with two arms, each arm coming from the end of
a distinctive bar of stars across its centre, is called a barred spiral.
Elliptical galaxies look like
bright footballs in space.
•
Irregular galaxies do not have a special shape. The two most
famous irregular galaxies are the Large and Small Magellanic Clouds
named after the explorer Ferdinand Magellan.
Photo credit: NASA
•
Journey through the cosmos Set 1
9
Our galaxy, the Milky Way
The galaxy in which we live is commonly known as the Milky Way.
It is called the Milky Way because it looks like a giant splash or river of
milk across a dark sky. But you probably haven’t seen it look like this,
unless you live somewhere a long way away from a town.
Until 150 years ago, the Milky Way was the most obvious thing in
the night sky. Light pollution caused by electric lights now makes
the sky around Earth so bright that it has become hard to see much
of the Milky Way.
What can you see of the Milky Way?
Try to see the Milky Way on a clear, dark night. What you see is actually
the centre of our Galaxy. (Write a capital letter at the beginning of the
word galaxy when you are referring to our own galaxy, the Milky Way.)
view from above
side view
Sun
Sun
1.
What kind of galaxy is the Milky Way?
2.
Describe the position of our Sun in our Galaxy.
_______________________________________
The Milky Way is thought to be a spiral galaxy and may be the special kind
of spiral called a barred spiral. Our Sun is situated almost at the outer rim
of the Galaxy, about two thirds of the way towards the end of one of the arms
of the spiral on its inner edge.
When you look at the Milky Way, you are really looking inwards
to the middle of our Galaxy. Using a telescope, Galileo was the first
to find that this milky band really consisted of thousands of individual
stars. In fact, the Milky Way is made of about 100 million stars.
Journey through the cosmos Set 1
10
What are quasars?
Out in the furthest reaches of the Universe, there are objects that may be
the brilliant hearts of very young, active galaxies. They may be small
and compact and are sometimes no bigger than our Solar System.
But they give out as much energy as a hundred or even a thousand
normal galaxies. These objects are called quasars.
The source of energy for a quasar is a mystery to astronomers but it is
thought that a quasar is powered by a massive black hole at its
centre.
To study some quasars means looking back to the infant Universe.
Maybe, normal galaxies – that, is spiral, elliptical and irregular
galaxies – started as quasars.
Exercise 2
Use information from Lesson 2 to complete the send-in exercise.
Journey through the cosmos Set 1
11
Lesson 3
Stars: the building blocks of galaxies
When you look at the night sky, you can see only about three thousand stars
of our own Galaxy with the naked eye. The darker the skies, the more stars
you can see. Of course, there are billions more stars but they are so far away.
You can see stars because they are luminous, which means that they give out
their own energy as light.
Each galaxy is a collection of many millions of stars which come in different
sizes, different colours, different brightnesses and different stages of their
life cycle. (Yes, just like you, a star has a life cycle – even though stars are
not alive!) But why do stars look different? Some of the differences are
due to the varying composition of stars. So what are stars made of?
What are stars made of?
Here is a simple diagram of the structure of our star, the Sun.
corona
a halo or crown
of gases
photosphere
the bright region
of the Sun that
you see
core of
intensely hot
hydrogen and
helium gas
There are also small amounts
of other elements such as
iron, calcium and sodium.
A star is composed of
________________________________________________________________________
__________________________________________________________________________________________________________
Turn to the answer pages to check your answer.
Journey through the cosmos Set 1
12
How do we know what a star is made of?
The light from a star is very, very weak by the time it arrives at Earth.
But, it can still reveal many of the star's secrets. How? Have you
ever made sunlight pass through a glass prism? Did a rainbow form?
Make your own prism
You can make your own simple prism or your teacher may supply
you with one.
For this activity, you will need:
•
a straight-sided clear glass (or a beaker from your Basic Science Kit)
•
scissors
•
a piece of cardboard about the same height as the glass
•
a sheet of white paper
•
a sunny day.
What to do:
1.
Fill the glass with clean water.
2.
Cut a long narrow hole, or slit, in the piece of cardboard.
3.
Place the glass on the white paper in front of a closed window
in a sunny position.
4.
Place the cardboard between the glass and the window and
move it until you have produced colours on the white paper.
5.
Which colours did you see?
About light
Normal white light is made up of different colours which form a rainbow.
A rainbow is called a spectrum and it is created by the splitting of light
into its different colours (or wavelengths).
White light splits as it passes through a prism (or a glass of water)
because the light is bent. This bending of light is called refraction
and the separation of white light into colours is called dispersion.
Journey through the cosmos Set 1
13
Study the diagram below that shows refraction and dispersion of white light.
It is a bit of a tricky diagram because it is drawn in three dimensions.
The numbers under the spectrum refer to wavelengths of light.
cardboard with slit
white light entering prism
prism
re
d
700
or
an
ge
ye
llo
w
600
gr
ee
n
bl
ue
500
in
di
go
vi
ol
et
400
1.
Trace your finger along the path of the light from the slit in the cardboard
into the prism then out of the prism, making a rainbow.
2.
What are the colours in the rainbow?
We usually write them from right to left.
3.
Use a clear ruler to study the direction of light as it travels through
the prism. Put your ruler along the top of the white light.
Can you see that the light bends when it enters the prism?
It does not travel straight ahead.
Now put your ruler on the edge of the coloured light as it travels
through the prism. (It doesn’t matter whether you use the ‘top’ edge
or the ‘bottom’ edge.) Notice that the coloured light bends again as it
leaves the prism.
4.
Write your own explanation of why you made a rainbow
in the activity on page 12.
Compare your answer with the ones in the answer pages.
Journey through the cosmos Set 1
14
Starlight and spectra
You have just studied the spectrum from our star, the Sun.
Scientists can refract (bend) and disperse (split up) light from other
stars to make spectra too. (Spectra means more than one spectrum.)
Starlight is gathered by a telescope and made to pass through
an instrument called a spectroscope. The spectroscope refracts
and disperses the starlight into its colours, making a spectrum.
But, starlight has some of the colours (or wavelengths) missing
which forms dark lines across the spectrum. If you could look
very closely at the rainbow formed from sunlight, you would be
able to see many fine dark lines because the Sun is a star.
A spectrum tells us a lot about the star, particularly:
•
the chemical composition of the star, by studying the dark lines
•
the temperature of the star, by observing which colours are brightest.
Journey through the cosmos Set 1
15
Lesson 4
The life cycle of a star
Do you remember the stages of the human life cycle?
The life of a star can be described using similar words to the human life
cycle with similar meanings.
What changes occur during a star’s life cycle?
Although a star does not have a life in the true sense of the word,
a star is very much like a person going through life stages.
Here are the main stages in a star’s life.
1.
birth
A cool newborn (newly formed) star is called a protostar.
2.
childhood
The star heats up as it increases in size.
3.
adolescence
The star is now hot enough for nuclear fusion to begin.
Nuclear fusion further increases the temperature of the star’s core.
(Nuclear fusion is the reaction that provides the star’s energy.
You’ll learn more about nuclear fusion on the next page.)
4.
maturity
A star spends most of its life in this stage, shining steadily
without changing.
5.
middle age
The star expands to become a red giant.
6.
old age
The star becomes unstable.
7.
death
The fate of a star and how long the star lives depends on its mass.
As you can see, stars like people, change as they age. However,
since a star ages over millions and sometimes billions of years,
it is very difficult for you to notice any visible changes.
And some stars, like people, spend their life with a companion
while others, like our Sun, live alone.
Journey through the cosmos Set 1
16
Over the next pages, you’ll read more about the life stages of stars.
As you read, identify the changes that are occurring and what can
be observed as a star moves from one life stage to another.
Underline or highlight information so that you can refer back to it
once you have read the entire lesson.
How is a star born?
Space is not empty although in many places it is extremely rarefied.
This means that space contains very few atoms. Nowhere in nature
is there a perfect vacuum (a region completely free from any matter).
The material between the stars is called the interstellar medium.
It is very important because it is the raw material for new stars.
It is mainly made up of:
•
gas particles such as hydrogen
•
dust particles which represent only about 1% of the interstellar medium.
The interstellar medium may be about as dense as having
five atoms of gas in a matchbox-size volume of space.
A protostar is created when a cloud of interstellar medium contracts.
This cloudy star nursery is called a nebula. As the cloud of gas
and dust continues to shrink, it becomes so hot and dense that
nuclear reactions are triggered causing the fusion (joining) of
hydrogen atoms to form helium gas. Nuclear fusion liberates
an enormous amount of energy. As long as there is hydrogen gas,
the star will keep shining due to the nuclear fusion processes within.
In a reaction called nuclear fusion,
two special hydrogen atoms
2
1
H
+
2
1
join to make
H
one helium atom
4
2
= protron
He
releasing energy
= neutron
A star has been born, and develops through childhood and
adolescence to maturity.
Journey through the cosmos Set 1
17
How will a star die?
The Sun is a good example of a medium-sized star.
How will a star like the Sun die?
When a medium-sized star like the Sun uses up its hydrogen,
it begins to die. But it will keep shining because it now uses helium
instead of hydrogen as the fuel. It also makes other familiar elements
such as carbon, oxygen, calcium, aluminium and finally iron.
As this occurs, the Sun will undergo dramatic changes in how it looks.
It will expand to the size of a giant, up to 100 times larger than the
present Sun. It will have a red colour because its surface temperature drops.
The corona (outer shell) of our Sun may reach beyond Earth's orbit
at this stage. It is now called a red giant.
What will happen to Earth? As the Sun grows closer and closer to Earth,
the oceans will evaporate, life will no longer exist, the rocks will vaporise
and Earth will finally fall into the Sun's core. When will this happen?
Not for about five billion years so there is no need to worry!
As the Sun expands, the core shrinks due to gravitational forces
crushing it to the size of Earth. The outer atmosphere is blown away
into space, forming a ring called a planetary nebula (but it has
nothing to do with a planet). The Sun is now very hot and it is called a
white dwarf. Over a long period of time, the Sun will die very quietly.
Eventually it will cool to a dead star called a black dwarf.
Of course, the description above is a very simplified view of the death
of the Sun. But it is a typical description for a medium-sized star.
The diagrams below represent some of a medium-sized star’s life stages
from maturity, through middle age and old age, to death.
Use the descriptions of life stages on page 15 and
the descriptions of stars above to label each diagram.
The first one has been done for you as an example.
Stage:
maturity
Stage:
____________________
Name:
star
Name:
____________________
Stage:
___________________
Stage:
____________________
Name:
___________________
Name:
____________________
Check your answers now.
Journey through the cosmos Set 1
18
What about stars that are much larger than our Sun?
Stars that are more massive than our Sun die in a very spectacular way
by forming a supernova. This is a gigantic, violent explosion.
The supernova can shine as brightly as an entire galaxy of stars.
Supernovae (or supernovas) have been rarely seen in our Galaxy
(about 3 every 100 years) but astronomers can see them occurring in
distant galaxies.
Photograph by David Malin
© Malin/Pasachoff/Caltech
The Crab Nebula shown below is a supernova remnant, a glowing nebula
of gas and dust exploded into space from the death of a large star
seen and described in 1054 AD. (Wouldn’t that have been exciting!)
In 1987, a supernova was discovered in the Large Magellanic Cloud.
It was so bright that it was visible to the naked eye for months.
Journey through the cosmos Set 1
19
What is the end result of a supernova?
What happens to a star after it has exploded depends on
how massive it is.
If the core of a star is between 1.5 and 3 times the mass of our Sun
then the core of the dying star will shrink until it is about 10 to
20 kilometres in size. It will be made entirely of neutrons.
The crushed ball of neutrons that survives is called a neutron star.
One teaspoon of this extremely dense star has a mass of about
a billion tonnes!
Are neutron stars visible?
A rapidly rotating neutron star radiates an intense narrow beam of energy,
especially radio energy. The beam sweeps across the Universe like a
lighthouse beam as the neutron star rotates. We can detect this kind of
dead star with a radiotelescope if Earth lies in the path of the beam.
The regular blinking, like an on-off signal, is the trademark of what
is called a pulsar. The name is short for 'pulsating radio source'.
Pulsars can rotate as fast as 1 000 times a second.
radio waves
rotating pulsar
radiotelescope
t
a
oE
rth
There must be
a pulsar out there!
Pulsars were first discovered in 1967 when unknown regular signals
were picked up coming from several parts of the sky. Initially they
were called LGMs, short for 'Little Green Men', because astronomers
were unsure of their origin.
Journey through the cosmos Set 1
20
The ultimate death of a star
If the core of the dying star is more than three times the mass of our Sun,
then it will keep on collapsing without stopping until it disappears
forming a black hole. This is the most mysterious object in the
Universe.
The gravitational force around a black hole is so powerful that matter
and even light cannot escape its pull. If anything gets too close, it gets
dragged in and remains trapped for eternity. What is a black hole like?
You could create a black hole situation if you could crush Earth
to the size of a large pea while still having all its original mass.
To escape a black hole, you would have to move faster than
the speed of light (greater than 300 000 km/s). In comparison,
a spacecraft must have an escape velocity of only 11 km/s
to escape from Earth's gravity and travel into space to other parts
of the Universe.
Journey through the cosmos Set 1
21
Finding a black hole (without getting too close!)
You cannot see a black hole but scientists can detect its presence by
the activity that goes on around it. Signs of a black hole include:
➀
➁
jets of matter and X-ray energy emerging from the centres of galaxies
➂
a disk of material dragged from a nearby star circling the 'hole'
like water going down a drain.
a doughnut-shaped collection of matter swirling rapidly around
an invisible centre
Number these three observations on the diagrams below.
jet of matter
and X-ray energy
black hole
star
black hole
gases from the
star’s atmosphere
doughnut-shaped
collection of
swirling matter
Check your answers.
Comparing the sizes of stars
In this lesson, you have used the words dwarf and giant to describe
the sizes of a star at different stages of its life cycle. Some stars even
change to become supergiants. How large are these stars?
•
A dwarf is much smaller than the Sun. For example, a white dwarf
could be as large as the Earth but its mass is still as great as the Sun’s.
•
A giant is 10 to 100 times larger than the Sun.
•
A supergiant is more than 100 times larger than the Sun.
But how big is a neutron star?
Journey through the cosmos Set 1
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Below are diagrams comparing the sizes of a neutron star, red giant,
white dwarf, a black hole and the Sun. Each diagram tells you
underneath it what objects are represented.
Write labels on the diagrams to show which object is which.
For example, in the first diagram, is the larger object the Sun or
the red giant? Label both objects in each diagram then check your
answers.
Sun and red giant
Sun and white dwarf
White dwarf and neutron star
Neutron star and black hole
Have you checked your answers?
Journey through the cosmos Set 1
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All those new words!
You have learned many new words and terms in this lesson, (protostar,
dwarf, nebula, black hole, gravity, pulsar, supernova, neutron, fusion,
supergiant, red giant, dust and gas). Can you find them below?
S
R
A
T
S
O
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P
B
U
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N
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L
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A
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K
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C
S
W
L
B
G
C
A
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A
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K
I
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H
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S
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I
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A
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Clues
1.
A cloud in space
2.
A star just ‘born’
3.
The name for gravitational force near Earth
4.
This word describes a special kind of star explosion
5.
A word that describes how stars produce energy
6.
Our Sun will become one of these
7.
Clouds in space are made of these two kinds of substances
and
8.
A huge star
9.
This kind of star is the very small, dense remains
of a star that was much larger than our Sun
10. A name for the star in clue 9 when it can be detected
by flashing beams of energy
11. Nothing escapes this
12. The final size of our Sun when it 'dies'
Check your answers before you continue.
Journey through the cosmos Set 1
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Describing the life cycle of a star
You will describe the life cycle of a star in the send-in exercise for this lesson.
So stop now and look back through the lesson at the information you marked.
In the space below (or on your own paper), construct a summary showing
the changes that occur to a star as it goes through its life cycle.
Use the boxes and hints below to help you.
Birth
A
forms from
when a
and
contracts.
Childhood and adolescence
Maturity
A steadily shining star, fuelled by nuclear
Middle age and old age
Death
The way a star ends depends on how much mass it has.
There are three ways that a star can die.
For a Sun-sized star …
For a star with a core up to three times the mass of our Sun …
For a star with a core more than three times the mass of our Sun …
Exercise 4
Complete the life cycle of a star in send-in Exercise 4.
Journey through the cosmos Set 1
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Lesson 5
Stellar colour, brightness and size
Stars are often described in terms of their colour or temperature,
their brightness and their size. But what do these things mean
when you think about something as big and bright as a star?
You’ll find out in this lesson.
Why do stars have different colours?
If you look closely at the stars, most of them appear white but
there are some that are distinctly red or blue. Why?
Stars have different colours because they have different
surface temperatures. In the Orion constellation, there are two stars
called Betelgeuse (commonly pronounced Beetle-juice) and
Rigel (pronounced Ri-jel). Betelgeuse is red in colour because
its surface is very cool but Rigel is blue because its surface is very hot.
This may seem confusing because we often associate red colour with
very hot things and blue with coolness. This is not the case with stars.
Have you noticed that when a piece of metal like iron heats up,
the colour changes to red to orange then yellow? If a metal can be
further heated, it becomes white hot then blue-white in colour
when it is extremely hot. Stars behave in a similar way.
Journey through the cosmos Set 1
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Why do stars have different brightnesses?
If a cool star is close to Earth, it will appear very bright.
Yet a larger star which is naturally much hotter and brighter,
but very far away, may appear dim by comparison.
A star's apparent brightness is influenced by its distance from Earth
as well as its size. A good example is the Sun which is only
average in temperature but very close to Earth. It appears to be
much brighter than all other stars but, of course, this is not the case.
Venus and the Moon are not stars so they are not luminous. Why do
you think they can still be given values for magnitude of brightness?
Did you suggest that Venus and the Moon reflect light? They cannot make
their own light but they can bounce back light that hits them.
Often, when we think of objects
that reflect light, we think of mirrors.
Mirrors bounce back all the light
that hits them.
Because the mirror is very smooth,
light is reflected in a precise way
and you see a clear image,
or reflection, of yourself.
light A light B
angle A
angle A
angle angle
B
B
mirror
mirror
mirror
mirror
Light bounces off a surface at the same angle
that it hits. This is called the law of reflection.
But all objects that you can see reflect light. If light bouncing off the object
did not reach your eyes, you would not be able to see the object at all!
Journey through the cosmos Set 1
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light energy from
a luminous source
reflected light
travels from the object
to your eyes
Draw a simple diagram to show why you are able to see the Moon.
There is an example in the answer pages.
The Moon appears to be very bright – after the Sun, it is the brightest
thing that you see in the sky.
Journey through the cosmos Set 1
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Why do stars have different sizes?
You've already seen some reasons why stars vary in size.
Why are some stars very small and others very big?
Did you refer to the changes in size that happen to stars during their life cycles?
You also learned that some stars are formed with more mass than others.
Remember, you found out about different 'star deaths' for stars that are
a similar size to our Sun, a little bigger and a lot bigger.
So how big are stars?
It is impossible for you to see that stars in the night sky have
different sizes. But, if you think of our Sun as having a value of
one solar diameter then you can compare how big or small other stars
may be. For example, a star that is three solar diameters would be
three times as big as our Sun.
Look at the table below.
Star
Comparative size
Sun
1 solar diameter
Vega
4 solar diameters
Rigel
a blue giant star in the Orion constellation
Betelgeuse
a red supergiant star in the Orion constellation
50 solar diameters
400 solar diameters
Sirius
the brightest star in the night sky
2 solar diameters
a white dwarf
the remains of a Sun-like star
0.01 solar diameters
a neutron star
the dead remains of a very large star
0.00001 solar diameters
How does the Sun compare?
_____________________________________________________________
Journey through the cosmos Set 1
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Our Sun is just an average-sized star. Even though it looks rather
impressive from Earth, there are billions of other stars like it.
Here is an activity that you can do to help you compare the sizes of stars.
You can make models using real objects or you can create the models
in your mind.
For the activity, you will need:
•
sheets of newspaper
•
scissors
•
a ruler
•
a pencil
•
a good eye for drawing circles (or a pair of compasses and
other circle-drawing equipment).
What to do:
1.
Make a circle with a 1 cm diameter to represent the size of the Sun.
2.
Make a circle with a 50 cm diameter to represent Rigel.
3.
Betelgeuse will be four metres in diameter.
(Too large to make with paper? You can if you try!)
4.
The white dwarf will only be one hundredth of one centimetre
in diameter, just a dot.
5.
The neutron star would be impossible to cut out because it is only
a one hundred thousandth of a centimetre. Would you need
a microscope to see the neutron star using this scale?
So let's summarise how our Sun compares with other stars.
How does our Sun compare?
The Sun is yellow in colour and average in size.
It has existed for about 5 billion years and will continue to do so
for another 5 billion years. A star like the very hot giant Rigel
will only live for about 20 million years. Hotter stars than Rigel
may exist for as little as 5 million years. Cool stars like the red dwarf
Proxima Centauri, which is the closest star to Earth, may exist for
100 billion years. However, Proxima Centauri is not visible from Earth.
Exercise 5
Turn to the send-in pages now.
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Journey through the cosmos Set 1
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Lesson 6
Cosmic distances
Are you beginning to get an idea of how big the Universe is?
Objects, their masses and the distances between them can be huge!
For example, it is useless to try to measure most distances in the Universe
using the 'Earth' unit kilometres. A kilometre is too small for such
enormous distances.
How do astronomers measure distance in space?
Instead of kilometres, astronomers use a unit called the light year
to measure distance in space. A light year (ly) is the distance that
light travels in one year. A light year is a very long distance because
light travels at the speed of 300 000 kilometres per second.
How far does light travel in one year?
Use a calculator to do the following calculation.
1.
Multiply 300 000 (which is the speed of light in seconds) by 60
to find out how far light has travelled in one minute.
2.
Then multiply your answer from Step 1 by 60
to find out how far light has travelled in one hour.
3.
Then multiply your answer from Step 2 by 24
to determine distance travelled in one day.
4.
Then multiply your answer from Step 3 by 365.25
to calculate how far light has travelled in one year.
5.
What is your answer?
_________________________________________________________________
There is a solution in the answer pages.
Journey through the cosmos Set 1
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Travelling to Alpha Centauri
After the Sun, Alpha Centauri is the closest visible star to Earth. It is
one of the pointers to the Southern Cross. This might make you think
that Alpha Centauri is fairly close to Earth. How far away is it really?
Alpha Centauri is 4.3 ly away from Earth.
How large is this distance in kilometres?
Did you multiply the number of kilometres in one light year (9 467 280 000 000)
by 4.3? The answer is close to 40 000 000 000 000, or 40 trillion kilometres.
Too big a distance to begin to imagine!
How long would it take to go to Alpha Centauri if you could get there
by foot, car, jet and space shuttle?
Using lines, match up the mode of travel with the correct speed
and with the correct time taken.
Mode of travel
Speed of space travel
Time taken
by foot
900 km/h
5 000 000 years
by car
6 km/h
160 000 years
by jet
28 000 km/h
45 000 000 years
100 km/h
750 000 000 years
by space shuttle
Do you think it is likely that humans will travel to Alpha Centauri
in the next 100 years? Why or why not?
Check your answers in the answer pages.
Journey through the cosmos Set 1
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What is an astronomical unit?
Astronomers have another unit that they use to measure distances
within our Solar System. It is called the astronomical unit.
An astronomical unit, or AU, is the average distance from Earth
to the Sun. It is equal to 150 million (150 000 000) kilometres.
How long does it take for light to travel one astronomical unit?
Remember, speed is a measure of how quickly something moves.
To find a speed, you need to know the distance from one place to
another and the time taken for the trip.
Speed can be written using a mathematical formula:
distance
speed = time
1.
Using this formula, calculate how long it takes for light
to reach Earth from the Sun. Remember that light has a speed
of 300 000 km/s.
2.
Your answer is a time measured in seconds.
What is this time in minutes?
3.
Why do you think the AU is used for distances within the
Solar System only, and not for distances in the Universe?
Check your answers now.
Journey through the cosmos Set 1
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How many astronomical units are equivalent to one light year?
Most people think that our Solar System is very large because
it takes many years for unmanned space probes to reach their
remote destinations. But, these distances are tiny in comparison
to the distance travelled by light in one year.
Use your calculator to carry out the calculation below.
Divide the number of kilometres in one light year (round up your
number to 9 500 000 000 000 for a simple calculation) by 150 000 000
which is the approximate number of kilometres in one AU.
Approximate your answer by expressing it in whole 'thousands' only.
Check your answer now.
Here is an activity to help you to demonstrate the difference between
light years and AU.
For this activity, you will need:
•
a piece of chalk.
What to do:
1.
Mark a point on the ground about one millimetre in size.
This represents one AU, the distance that Earth is from the Sun.
Not very big is it?
2.
Take 63 steps away making each step about a metre in size.
This new distance represents the size of one light year.
3.
If you walk about another 210 metres (a total of 273 steps),
you will now have walked the scaled distance from the starting
point to the nearest visible star to us other than our Sun.
If astronomers had to use the AU as the only unit of distance then
Alpha Centauri would be over 270 000 AU from Earth.
Using 4.3 light years is much easier, isn't it?
The most distant planet, Pluto, is about 39.5 AU from the Sun so
light would take only 39.5 x 8.3 minutes or about 5 hours 29 minutes
to reach Pluto. Do you agree that it would not be appropriate
to use the light year for distance measurement within the Solar System?
Journey through the cosmos Set 1
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How would you measure the distance to the Moon?
Since the Earth-Moon distance is only about 384 000 kilometres
then you would not measure the distance using light years or AUs.
The kilometre would be the best unit for measurement because
the distance is so small.
How many times bigger is an AU than the distance between the Earth
and the Moon? On your calculator, divide 150 000 000 km by 384 000 km.
Check your answer.
Measuring distances to stars and galaxies
As Earth moves in its orbit around the Sun, nearby stars appear to shift
in their position back and forth against the background of the more
distant stars. This is an illusion; the nearby stars are not really moving.
Try this.
1.
Close one eye and hold up a thumb at arm's length to cover
any distant object such as a photograph or ornament in the room.
2.
Without moving your thumb, open your eye and close the
other eye instead.
3.
What did you notice?
Did the object appear to move even though you did not move your thumb?
Similarly, if you hold a pencil upright at arm's length and alternately
close each eye, the pencil will appear to jump back and forth.
This kind of illusion is called parallax shift and also occurs when
astronomers view a star from opposite ends of the Earth's orbit.
After finding the angle of parallax of the star, trigonometry
(mathematics using triangles) can be used to calculate the distance
to the star. This kind of distance calculation, however, is only possible
for stars up to 980 light years away.
Journey through the cosmos Set 1
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So how far away from Earth are they?
Get a feel for the distances in our Universe by comparing the
distances to some stars and galaxies in the following tables.
Nearby star
Found in the
constellation called
Sirius
Canis Major
Vega
Lyra
26
Aldebaran
Taurus
68
Spica
Virgo
218
Betelgeuse
Orion
518
Antares
Scorpius
520
Rigel
Orion
900
Galaxy
Distance away
(in light years)
8.6
Distance away
(in light years)
Large Magellanic Cloud
160 000
Small Magellanic Cloud
200 000
Andromeda
2.2 million
Centaurus A
30 million
Whirlpool
35 million
Sombrero
41 million
The view from here
It is very hard to judge distances when you look out into space.
For example, you probably think of the Southern Cross as a familiar
pattern of stars. Do you imagine that all the stars in the constellation
are close together, the way they were drawn at the beginning of this set?
You've probably guessed that they are not. The two pointer stars are
called Alpha Centauri and Beta Centauri. Alpha Centauri, as you have
learned, is only 4.3 light years away. Beta Centauri is over 400 light
years away. Yet when you look at them, they appear similar in distance
and brightness.
Journey through the cosmos Set 1
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Looking back in time
When you look at the blue star Rigel in the constellation Orion at night,
you really see it as it was 900 years ago. How can this be?
Rigel is 900 light years away so light must travel for 900 years
before it reaches Earth.
The way you see Rigel tonight is actually what it looked like
all that time ago. Today, it could come to the end of its existence
in a spectacular supernova explosion but you would have to wait
900 years before you can witness this brilliant event!
(Sorry, if it does explode today, you won't be on Earth to see it!)
When astronomers look towards the edge of the visible Universe,
they are reaching back in time to a very young Universe.
Galaxies that are billions of light years away must have formed
early in time. They may not exist today but we still see them because
their light is still reaching us from all those billions of years ago.
Set 1 of this unit has been about how BIG scientists think the Universe is.
The last send-in exercise for this set will help you to show your teacher
how well you understand this current model for the Universe.
Exercise 6.1 and 6.2
Complete send-in Exercise 6.1 and 6.2 now.
Journey through the cosmos Set 1
38
Checking your progress
What are the important ideas from Set 1?
Some things to remember
•
There have been different models of the Universe throughout history.
•
People of different centuries and different cultures have contributed
to the development of the current model of the Universe.
•
The Universe has existed for a very long time. By comparison,
the life forms that are familiar to you are very recent.
•
Luminous objects, such as stars, are able to make their own light
by nuclear fusion.
•
Galaxies contain billions of stars. There are different kinds of
galaxies – spiral, elliptical and irregular.
•
Stars have a life cycle. They may go through stages such as
protostar, mature star, red giant, white dwarf, black dwarf,
supernova, neutron star and black hole. The way stars die
depends on their mass.
•
Stars do not always give out light; as neutron stars, they may
emit radio waves.
•
Stars vary in colour (temperature), brightness and size.
•
You can only see non-luminous objects, such as planets and
the Moon (and your lunch), because these things reflect,
or bounce back, light.
•
The bending of light is called refraction.
•
The splitting of white light into its colours is called dispersion.
•
The soaking up of light is called absorption. When light is absorbed,
it changes into other forms of energy.
•
A light year is much further than an AU (astronomical unit)
which is much longer than a kilometre.
•
The Universe is very BIG!
Journey through the cosmos Set 1
39
Suggested answers
Lesson 1
Page 5
Some models of the Universe
Time and the Universe
You can match the times because the events are in order of time.
Lesson 3
Page 11
Stars: building blocks of galaxies
What are stars made of?
Did you decide that stars are mainly made of (intensely hot) hydrogen and
helium gas with a very small percentage of other elements like iron, calcium
and sodium?
About light
Page 13
2.
The colours of the rainbow are usually listed as red, orange, yellow, green,
blue, indigo and violet.
If you'd like to remember these colours and their order, think of the name
Roy G Biv. Each letter of this boy's name will remind you of a colour.
Journey through the cosmos Set 1
40
Lesson 3 continued
4.
Lesson 4
Page 17
Here is a sample answer.
White sunlight was bent when it moved from the air into the water in
the glass. As the light bent, the colours in white light were split apart.
This refraction (bending) of light produced the coloured rainbow
(dispersion).
The life cycle of a star
How will a star die?
These diagrams attempt to represent some parts of the information you have
just read. They are not really diagrams of what the stars might look like.
Page 21
Stage:
maturity
Stage:
old age
Name:
star
Name:
white dwarf
Stage:
middle age
Stage:
death
Name:
red giant
Name:
black dwarf
Finding a black hole (without getting too close!)
➀
jet of matter
and X-ray energy
black hole
➂
star
black hole
➁
gases from the
star’s atmosphere
doughnut-shaped
collection of
swirling matter
Journey through the cosmos Set 1
41
Lesson 4 continued
Page 22
Comparing the sizes of stars
red
giant
Sun
Sun
Sun and red giant
white dwarf
Sun and white dwarf
neutron star
white
dwarf
neutron star
black hole
White dwarf and neutron star
Page 23
Neutron star and black hole
All those new words!
1.
nebula
S
R
A
T
S
O
T
O
R
P
2.
protostar
B
U
N
O
R
T
U
E
N
E
3.
gravity
L
T
P
H
G
D
L
D
E
T
4.
supernova
A
N
K
E
C
S
W
L
B
G
5.
fusion
C
A
O
F
R
A
S
L
U
P
6.
red giant
K
I
F
I
R
G
P
G
L
O
7.
dust and gas
H
G
C
F
S
O
I
S
A
D
8.
supergiant
O
D
E
N
L
U
A
A
L
U
9.
neutron
L
E
M U
O
D
F
I
N
S
10. pulsar
E
R
Y
T
I
V
A
R
G
T
11. black hole
S
A
V
O
N
R
E
P
U
S
12. dwarf
Journey through the cosmos Set 1
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Lesson 5
Page 27
Stellar colour, brightness and size
Why do stars have different brightness?
You are able to see the Moon because it reflects sunlight to your eyes.
light energy
from the Sun
light energy is reflected
by the Moon
reflected light
travels to your eyes
Lesson 6
Page 31
Cosmic distances
How far does light travel in one year?
5.
Page 32
300 000 x 60 x 60 x 24 x 365.25 = 9 467 280 000 000 kilometres
(or 9.46728 x 1012 km)
Travelling to Alpha Centauri
It is unlikely that humans will travel to Alpha Centauri in the next century
because our spaceships cannot travel fast enough and Alpha Centauri is
too far away. At the speed humans can travel, it would take much too long
to traverse the long distance.
What you are saying in your answer is the time of travel relies on
the distance to be travelled and the speed you can go.
Journey through the cosmos Set 1
43
Lesson 6 continued
Page 33
How long does it take for light to travel one astronomical unit?
1.
There are two ways you could do the calculations.
Rearrange the equation:
Substitute into the equation:
distance
distance
speed =
so
speed =
time
time
150 000 000
distance = speed x time and
300 000 =
time
distance
time = speed
500
1 = time
150 000 000
=
300 000
So time = 500 seconds
So time = 500 seconds
Page 34
2.
To change seconds to minutes, divide your answer by 60.
500
= 8.3 minutes
60
3.
Distances in the Universe outside of the Solar System are much too
large to be measured in AU. An AU is really a short distance.
How many AU are equivalent to one light year?
kilometres in 1 ly
number of AU in one light year = kilometres in 1 AU
9 500 000 000 000
=
150 000 000
= 63 333
So there are more than 63 thousand AU in every light year.
Page 35
How would you measure the distance to the Moon?
kilometres in 1 AU
number of Earth-moon distances in one AU = kilometres between Earth and Moon
150 000 000
= 384 000
= 390.625
So 1 AU is more than 390 times the distance between Earth and the Moon,
or 1 AU is about 390 times larger than the Earth-Moon distance.
Journey through the cosmos Set 1
44
Journey through the cosmos Set 1
45
Send-in page
Name
______________________________
Lesson 1:
Some models of the Universe
Exercise 1.1
Some scientists and scientific ideas in history
The models that scientists have used to describe the Universe
have changed throughout history. Scientists continue to collect
observations and to test their ideas so that their explanations and
theories become more and more useful for making predictions.
The people listed below have been important in describing
how the Universe works:
Aristarchus (260 BC) Copernicus (1473-1543) Newton (1642 - 1727)
Aristotle (384-322 BC) Galileo (1565 - 1642)
Ptolemy (100-170 AD)
Brahe (1546 - 1601)
Kepler (1571 - 1630)
Place them in order of appearance in history in the column below
called 'Astronomers' with respect to their contributions to astronomy.
Astronomers
Key terms
1
__________
_____________________________________________________________
2
__________
_____________________________________________________________
3
__________
_____________________________________________________________
4
__________
_____________________________________________________________
5
__________
_____________________________________________________________
6
__________
_____________________________________________________________
7
__________
_____________________________________________________________
8
__________
_____________________________________________________________
Each astronomer can be remembered by key terms that are important
in describing their Universe models. These key terms are:
accurate observations
geocentric
heliocentric
elliptical orbits
gravity
telescope
epicycles
Select terms from the list to highlight each astronomer's model. Write them
in the column above called 'Key terms'. Some words can be used for more than
one astronomer and some astronomers have more than one term.
Journey through the cosmos Set 1
46
Exercise 1.2
1.
Different ideas to describe observations
When historians study ancient civilisations and cultures, they almost
always discover a knowledge, and usually a reverence, for the Universe.
Here is a description of how ancient Babylonians understood and used
what they saw in the skies. (The Babylonian civilisation was in the area of
Iran and Iraq and lasted from about the eighteenth to the sixth century BC.)
The sky was created and ruled by a god called Marduk who
controlled the Sun, Moon, planets and stars by following
well-laid and carefully documented laws and plans.
Feasts and religious ceremonies were performed in
accordance with positions of the Moon, Sun and planets.
Detailed almanacs were kept to record these positions and
to predict future positions. The earliest record of an
observatory specifically for watching the sky is from Babylon.
Scholars of this middle eastern kingdom travelled to
neighbouring countries, sharing and gaining information.
For example, there are important similarities between the
knowledge of the Egyptians and the Babylonians.
The accumulated knowledge from middle eastern civilisations such as the
Babylonians was important in the development of models of the Universe.
For example, Ptolemy had an Egyptian background. Most major advances
in astronomy during the first 1 500 years AD were made in or near Arabia,
in the middle east. This Arabic astronomical knowledge was important
for the development of ‘new’ models, such as Copernicus’ model.
Use information from the passages above to answer these questions.
(a) How did ancient Babylonians explain their observations of the sky?
(b) How did ancient Babylonians contribute to a model of the Universe?
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Name
Lesson 2:
Exercise 2
______________________________
Galaxies
Investigating deep space
With the assistance of the Hubble Space Telescope, it has been possible
to produce images of extremely faint, very distant objects reaching back
billions of years in areas of the Universe that appeared to be ‘empty’.
Study the picture below representing a photograph taken of deep space
by the Hubble Space Telescope showing hundreds of galaxies.
Like an astronomer, you can use a magnifying glass or hand lens
to help locate the different kinds of galaxies. All the dots in the field
of view are also galaxies but they are too small to be easily identified
because they are so distant.
1.
2.
3.
Circle the spiral galaxies that you find.
How many were there?
_________
Draw a square around the elliptical galaxies.
How many did you find?
_________
There are two irregular galaxies. Draw a triangle around them.
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Journey through the cosmos Set 1
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Lesson 4:
The life cycle of a star
Exercise 4
Construct a flow chart to tell the simplified story of the life cycles of stars.
The outline for the flow chart is shown below.
Separate the boxes on page 53 and glue the information
into the correct places in the flow chart.
The life cycle of stars
average-sized star
1.5 to 3 times
average size
Journey through the cosmos Set 1
more than 3 times
average size
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Cut the boxes below apart and use them to complete the flow chart
in Exercise 4.
a star bigger than
a black hole is formed the Sun results in
a supernova and
fusion of hydrogen
fuels the star for
many millions of
years until
death results in
a white dwarf and
finally a black dwarf
a star many times
bigger than the Sun
a star forms in
results in a supernova a nebula and
and
a neutron star called
a pulsar is formed
in the supernova
remnant
a Sun-size star
becomes a red giant
then
Journey through the cosmos Set 1
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Journey through the cosmos Set 1
53
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Lesson 5:
Name
______________________________
Stellar brightness and size
Exercise 5
In Set 1, you have been revising and extending your ideas about light.
You have read about and considered examples of absorption, reflection,
refraction and dispersion. The columns below contain these words,
their meanings and simple diagrams to show what is happening to light.
Draw lines to match each word in the first column with its meaning and
with a diagram representing the meaning.
light comes
absorption
bouncing back light
(when light is absorbed)
light goes
light comes
reflection
soaking up light
(when light is reflected)
light
light
light goes
goes
goes
light
light comes
refraction
(when light is refracted)
splitting white light
into colours
light goes
light comes
dispersion
bending light
(when light is dispersed)
Journey through the cosmos Set 1
light
is gone
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Journey through the cosmos Set 1
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Send-in page
Lesson 6:
Name
______________________________
Cosmic distances
Exercise 6.1
1. Near or far?
Throughout Set 1, you have read about where some objects are in space
compared with the position of Earth. Do you think you have an idea
of which objects are close and which are far away?
Number the objects listed below from 1 for the closest one
to 6 for the most distant from Earth.
_____
the Sun
_____
a quasar
_____
the Moon
_____
Alpha Centauri
_____
Large Magellanic Cloud
_____
the centre of the Milky Way
2. Which units would you use?
Which unit of distance would you select to best measure the distances
to the following cosmic objects?
Write the abbreviation for your choice of unit – km (kilometre),
AU (astronomical unit) or ly (light year) – beside each object.
_____
the distance to the Sun
_____
the distance to the Moon
_____
the diameter of the Milky Way
_____
the diameter of our Solar System
_____
the distance to the next closest star (after the Sun)
You’ll find out the best unit for measuring the size of the Universe in Set 2!
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Exercise 6.2
Set 1 has tried to give you an astronomer’s perspective of the Universe.
Use the questions below to help you summarise your ideas about
what the Universe is like.
1.
How big is the Universe?
2.
How old is the Universe?
3.
What are some objects in the Universe?
4.
What is most of the Universe like?
Journey through the cosmos Set 1