"Space Is Big. You Just Won't Believe How Vastly, Hugely, Mind-Bogglingly Big It Is…"

Douglas Adams, Hitchhikers Guide to the Galaxy.

True or false?

There is no gravity on the moonThe sun is nearer to us in the summer.There are no stars above us in the daytimeTwo planets are closer to the sun than the earthThe planets go round the EarthThe moon takes about a month to go round the earth.A galaxy is a special type of star.We know what the solar system looks like from the outside because people have travelled outside the solar systemWe see different stars at different times of the night because the stars due to the Earth’s rotationThe nearest stars are about 100 times further away than the sunSome planets are made of gasAstrology is the study of how the planets control your destiny.We have summers and winters because of the tilt of the earth.The Earth spins on its axis once a year.The Earth orbits the sun once a day.Other stars have planets.Telescopes are put up mountains so that they are nearer to the stars.

Check if you are right – answer in the back of the booklet.

Solar system.

Our solar system consists of our star (the sun) and everything that is bound to it by gravity. This includes:

Planets; Dwarf planets; Moons; Asteroids; Comets and Meteoroids.

It is one of billions of solar systems and is located in an outer spiral arm of the Milky Way Galaxy.

This diagram shows the planets of the solar system. The distances are shown is astronomical units (I AU = 149.9x109m = standard distance from the Earth to the Sun)

SPACE

It also shows how long light would take to travel from the sun to that planet.

(This diagram also shows Pluto – which is NOT a planet!)

Complete this table.

Planets in order from the sun Distance from the Sun (in AU) How does light from the sun take to reach it?

The planets are split into 2 categories –

the inner rocky planets the outer gas giants.

Inner rocky planet Outer gas giants

What about poor Pluto?

In 2006 the International Astronomical Union (IAU) demoted Pluto from planet to dwarf-planet. So first we need to know what the new definition of a planet it.

The IAU defines a planet as a celestial object that:

Orbits the central star – in our case the Sun Has sufficient mass to assume hydrostatic equilibrium – this is just a fancy way to saying they have sufficient

mass to be roughly spherical.o Bonus information – planets aren’t spherical they are squished slightly (they are bigger around the

equator) this is called an oblate spheroid – but for GCSE physics they are considered spherical Has “cleared their neighbourhood” around their orbit – there is nothing else on the same orbit.

The definition of a dwarf-planet is very similar – the only difference is in the final point.

A dwarf planet is an object:

In orbit around the central star Is massive enough to have its own gravity pull itself into a round (or nearly round) shape. A dwarf planet may also orbit in a zone that has many other objects in it. For example, an orbit within the

asteroid belt is in a zone with lots of other objects.

Pluto isn’t the only dwarf planet in the solar system. There are 5 officially recognised dwarf planets. In size order these are:

1. Pluto2. Eris 3. Makemake 4. Haumea.5. Ceres – used to considered an asteroid between Mars and Jupiter

Questions.

1 List the planets in our Solar System in order from the Sun.

2 Where is the asteroid belt situated?

3 In your own words define a planet.

4 Why is Pluto a dwarf planet?

5 What is the name of our galaxy?

6 Use the following information to answer the questions below.

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

mass (1024 kg) 0.330 4.87 5.97 0.64 1898 568 86.8 102

diameter (km) 4879 12104 12756 6792 142984 120536 51118 49528

density (kg/m3) 5427 5243 5514 3933 1326 687 1271 1638

Gravity (m/s2) 3.7 8.9 9.8 3.7 23.1 9.0 8.7 11.0

Mean temperature (°C)

167 464 15 –65 –110 –140 –195 –200

Surface pressure (bars)

0 92 1 0.01 Unknown Unknown Unknown Unknown

Ring system No No No No Yes Yes Yes Yes

I. Why is the temperature of Venus much greater than that of Mercury, even though it is further from the Sun?

II. Which planet has the largest gravitational force?

III. Which planet has the greatest volume?

IV. Which planets have rings? Explain what the rings are.

Life Cycle of a star.

Like most things, stars are born, they live, and then they die. All stars form the same way, but what happens to them as they die depends on how massive they way.

All stars form out of clouds of dust and gas – called nebula. The particles in this cloud and moving around as they bump into each other small clumps form. As the

particles are putted together by their own gravity, the particles speed up and increase in temperature. The cloud starts to spin.

Eventually the clumps become hot enough to glow – this called a protostar – a star to be. As more material gathers and the protostar become denser and hotter, if the star becomes dense and hot

enough hydrogen atoms fuse together to form helium and the star is born. The star spend most of it’s life in this phase – called the main sequence. The outwards pressure from the fusion stops the star collapsing further.

Some material is left over from this and is still in a spinning dust cloud – this will go on to form planets and asteroids. (Which is why the planets are all found on the plane of the Sun’s equator)

When a star runs out of hydrogen it is the end of the main sequence, it collapses further reaching higher temperatures where it can now fuse helium to make the heavier elements up to iron. The stars are now red giants.

What happens now depends on the mass of the star – they are split into three categorieso Sun like stars – mass up to 1.5 solar masseso Large starts – mass between 1.5 – 5 solar masses e.g. Rigelo Giant stars – mass greater than 5 solar masses e.g. Beetlejuice

Sun-like stars Large star Giant starsWhen there are no more light elements in the core fusion stops

When they run out of helium they swell into red supergiants.

There is no radiation preventing collapse due to gravity.

Then they collapse, this compression is suddenly reversed by a giant explosion called a supernova.

As it collapses it heats up to form a white dwarf.

Elements heavier than iron are created in this explosion

Over time this cools down to a black dwarf – there has not been enough time in the universe for this to happen yet.

Over time they collapse down to a star containing on neutrons – a neutron star.

Collapses down further to create a black hole, an object with a gravitational field so strong nothing can escape – not even light.

Write definitions for all the words in bold. (There is a glossary at the back of the booklet to help you but please write using your own words)

Questions.

1 When a star is in its main sequence, what forces are acting and why is the star stable?

2 Explain how light and heavy elements are present in the planets in our Solar System.

3 During fusion, four hydrogen nuclei fuse to form one helium nucleus and there is a loss of mass of 0.7%. Fusion only takes place if the hydrogen nuclei are moving very fast. The energy released can be calculated using Einstein’s famous equation: E = mc2 where c is the speed of light = 3 108 m/s and m is the loss in mass.

Use this equation to calculate the energy released when 2 g of hydrogen fuses to form Helium.

4 Use the information in the table below to answer the following questions.

Mass of star

(Sun 1)

Lifetime of star (millions of years)

Surface

Temperature (K)

A 0.5 200,000 4000

B 1 10,000 6000

C 3 500 11000

D 15 15 30000

a Describe and explain the relationship between the lifetime of a star and its mass, remembering that a star with a higher surface temperature also has a higher core temperature and pressure

b What is most likely to happen to the star B at the end of its lifetime?

c What is most likely to happen to the star C at the end of its lifetime?

d What is most likely to happen to the star D at the end of its lifetime?

5. Put the following sentences into the correct order.

A. The core of the cloud starts to shine and is now a protostar B. As the collapse continues the core reaches 10 million K, and nuclear fusion begins. The protostar has

become a star.C. The interior of the dust cloud has begun heating, and is about 10,000 K.D. The star continues to contract and increase in temperature, until it is in equilibrium – gravity is

balanced by radiation. The star has reached the Main Sequence and will remain there as long as it has hydrogen to fuse in its core.

E. Star formation happens when part of a dust cloud begins to contract under its own gravitational force; as it collapses, the centre becomes hotter and hotter.

F. Planetary formation has begun, but the protostar is still not in equilibrium–all heating comes from the gravitational collapse

Answer: ________________________________

Satellites and orbits

A satellite is an object that is in orbit around something other than the sun. Satellites are divided into two categories: natural and man-made. Moon and ring-systems are natural satellites, there are currently 181 known moons in our solar system. Only 4 planets and dwarf planets don’t have a moon – Mercury, Venus, Makemake, and Ceres.

For both artificial and natural satellites the force that keeps them in orbit is the same – the force due to gravity.

Gravity always acts towards the centre of the massive object – this is called a centripetal force.

If the object is moving perpendicular to this force its motion is changed by the force.

It will move in a circle. The motion of an object in orbit is always at right angles to the

force due to gravity. A satellite is always experiencing an acceleration towards the

centre of the circle.

A satellite in a stable orbit move at a certain height above the Earth. To stay in this radius of orbit the satellite has to move at the correct speed.

If the speed slows the radius of the orbit will decrease. If it decreases too much it will enter the Earth’s atmosphere, which will slow it further.

If the speed increases then the orbit radius will have to increase to stay in a stable orbit.

This is true for moon and planets around the sun as well as artificial satellites.

Geostationary satellites orbit at about 36,000km about surface of the Earth with a period of 24hr. This means they stay above the same place on Earth surface. These are often used for communications.

Question

1 Define a satellite

2 Explain why a satellite is accelerating even though its speed is not changing?

3 Using a diagram show the orbit of a satellite and draw on the direction of the force, the acceleration and the motion.

4 GPS satellites orbit the Earth about once every 12 hours. Write and explain if a GPS satellite is above or below

I. A geostationary satellite

II. A weather satellite with a period of 2hrs.

5 At what height must a satellite be placed above the Earth’s surface in order for it to be in a geostationary or geosynchronous orbit?

6 The radius of the earth as 6400km. Use the equation C=2πr to estimate the orbital speed of a satellite that was placed at an altitude of 15000km above the surface of Earth and takes 500 minutes to complete the orbit?

The expanding universe

Before discussing the expanding universe we need to look how moving affects the sound of a moving object.

Think about a moving car.

• The car’s engine produce sound waves.

• If a fast moving car travels towards you there is a noticeable change in the pitch of the sound waves you – it sounds higher pitched.

• As the car passes the frequency of the sound waves appears to change from a high frequency to a low frequency.

This is known as the Doppler Effect.

Stationary car.

• The circular lines are wave-fronts.

• The distance between wave-fronts represents the wavelength of the waves.

• The centre of each wave remains in the same place because the car does not move

Car moving towards you.

• When the car moves towards the observer, the centres of the waves moves towards the observer

• The wave-fronts are squeezed together.

• The wavelength of the waves decreases.

• The frequency of the waves increases.

Car moving away from you.

• When the car moves away from the observer, the centres of the waves moves away from the observer

• The wave-fronts are stretched out.

• The wavelength of the waves increases.

• The frequency of the waves decreases.

Complete this table.

Car moving towards you Car moving away from youWavelengthFrequency

Light

The same effect can be observed if a light source is moving towards or away from the observer.

• When a source of light is moving towards an observer the wave-fronts of light are squeezed together. The wavelength of the light decreases. Towards the blue end of the spectrum.

• When a source of light moves away from an observer the wave-fronts are stretched out. The wavelength of the light increases. The light appears to be redder in colour.

Red-shift is the change in colour of light waves caused by a source of light moving away from an observer.

Fill in the gaps

If a star or galaxy is moving _____________________ the Earth, the _____________________ of the light waves will be increased. This will mean that the light will appear _____________________ than it would were the source not moving relative to the Earth. This change in wavelength is called ____________-____________ .

The _____________________ a galaxy is moving away the greater this effect.

Light from galaxies

• In the 1920’s Edwin Hubble was able to observe the light from distant galaxies, using the world’s largest telescope at that time

• He discovered that light from distant galaxies appears redder in colour than light from our own galaxy, The Milky Way.

• Hubble measured the distance to several galaxies and the red-shift of these galaxies.

• This graph shows that size of the red-shift of light from a galaxy is proportional to the distance to the galaxy.

• Since the red-shift of light increases as speed increases, this graph shows that:

The further a galaxy is from us the faster it is moving away from us.

The universe is expanding.

The expanding universe.

• In a Universe that expands galaxies that are further apart move apart faster.

• This matches what Hubble saw.

In the expanding universe:

• The galaxies themselves do not expand because they are held together by gravity.

• The galaxies simply move further apart from each other.

Fill in the gaps

Astronomer Edwin Hubble discovered that:

1. light from distant galaxies was _ _ _ - _ _ _ _ _ _ _

2. the _ _ _ _ _ _ _ a galaxy is away from Earth, the _ _ _ _ _ _ the red-shift

The conclusion is

distant galaxies are moving _ _ _ _ from Earth (ie receding)

the greater the distance from Earth, the _ _ _ _ _ _ _ the speed of recession.

As there is no reason why the Sun is special place in the Universe, we conclude that

the whole Universe is _ _ _ _ _ _ _ _ _ .

Questions.

1 What is the Doppler Effect?

2 What is red-shift?

3 What happens to the light a galaxy gives off if the galaxy is moving away from us?

4 What is happening to the size of the Universe?

5 Galaxy X has a larger red-shift than Galaxy Y. Which galaxy, X or Y is….

a) Nearer to us.

b) Moving away faster.

6 What happens to the light a galaxy gives off if the galaxy is moving towards us?

7 Explain why distant galaxies having a larger red-shift is evidence of an expanding universe.

The beginning and the end

After Hubble explain the observed red-shift and expanding universe two competing theories were developed to explain this.

Steady State Theory – the universe does not fundamentally change

Big Bang Theory – the early universe is very different from the universe now

Steady State theory.

• A group of three scientists, Fred Hoyle, Herman Bondi and Thomas Gold, suggested a theory of the universe called the Steady State Theory.

• In this theory the universe was viewed as being “eternal and unchanging”. How can the Universe be expanding but not changing? Think of a stream of water running from a tap. From moment to moment the stream of water looks the same. But the stream of water is made up of different water molecules

The theory said that:

• The Universe had been expanding forever

• There was no beginning to the Universe

• The Universe will continue to expand forever

• There would be no end to the Universe

Big Bang theory

As the Universe is expanding now, the Big Bang theory says that it is natural to think that sometime in the past the Universe must have been much smaller than it is now.

The theory said that:

• The Universe began in a giant explosion.

• The Big Bang created space and time as well as all the matter we see in the Universe.

• The Universe has been expanding ever since.

Summarise the two theories below.

Steady state Big bang

Both theories made predictions about what the earlier universe would look like and then observers would check to see if they fitted the observations.

Galaxies:

• Predictions:

Steady State theory: on average galaxies look the same everywhere

Big Bang theory: far away galaxies look different from galaxies nearby.

• Evidence:

The Hubble Space Telescope shows that far away galaxies are different from galaxies nearby

• Conclusion:

The Big Bang theory is more likely to be correct

Cosmic Microwave Background Radiation (CMBR):

• High energy gamma radiation was created just after the big bang, when the universe was much hotter.

• Over time, it has stretched to longer and longer wavelengths and is now microwaves.

• This can only be explained by the big bang theory

How will the universe end?

Will the universe keep expanding forever – the Big Yawn? Or start to shrink again – the Big Crunch?

It all depends on the density of the universe. If the density is sufficiently great the universe will stop expanding.

What force would pull everything back together into a big crunch?

Dark matter and dark energy

If stars were the only mass in a galaxy then it would spin much quicker. So there must be a mass that we can’t see – this is called dark matter.

If the density of the universe is less than a critical amount, it will _ _ _ _ _ _ forever.

If the density of the universe is _ _ _ _ than this critical amount, it will stop expanding and go into reverse.

Evidence suggests that the expansion of the universe is actually accelerating! If this is the case, then there must be an unknown energy that is driving this acceleration. This unknown energy is call dark energy.

Questions.

A key piece of evidence for the Big Bang is ‘red-shift’. A simple model of this is shown below. The light can be thought of as being a star or even a galaxy.

1 When light is examined by astronomers, spectral lines on absorption spectra tell them about the speed and direction of motion of the galaxy being observed.

The spectral lines for the Sun and a nearby galaxy are shown below.

a Explain whether the galaxy shown is moving towards or away from the Sun.

b Describe how the spectral lines would appear different if the same galaxy was moving

i at a greater speed;

ii in the opposite direction.

2 In 1929, Edwin Hubble produced evidence to support the Big Bang theory. He did this by plotting a graph of the speed of galaxies against their distance from the Earth. The graph is shown below.

 

a State what the graph shows about the relationship between the distance of a galaxy and its speed.

b Explain how the graph suggests that the Universe is expanding

c i Explain how you could determine an age for the Universe from the data on the graph.

ii Calculate a value for the age of the Universe from the graph.

3 Evidence for the age of the Universe, in support of the Big Bang, includes:

• the cosmic microwave background radiation (CMBR)

• the proportion of hydrogen and helium present in the Universe

• red-shift.

Explain the important role played by the CMBR in suggesting that the Universe started in a Big Bang.

Answers.

True or False:

There is no gravity on the moon False – gravity is caused by 2 masses attracting each other. As the moon has mass it has gravity. It is about 17% as Earth’s.

The sun is nearer to us in the summer. False for us in the Northern Hemisphere. (True is you were in the Southern hemisphere)

There are no stars above us in the daytime False – the stars are always there, we just can’t always see them.

Two planets are closer to the sun than the earth True – Mercury and VenusThe planets go round the Earth FalseThe moon takes about a month to go round the earth. True. A galaxy is a special type of star. False – a galaxy is a collection of many millions/billions of

stars We know what the solar system looks like from the outside because people have travelled outside the solar system

False – the furthest manmade spacecraft is Voyager 1 launched in 1977 which has left the solar system (it is 14,000,000 miles away from the sun) but no people are aboard!

We see different stars at different times of the night because the stars due to the Earth’s rotation

True

The nearest stars are about 100 times further away than the sun

False – The nearest stars to Earth are in the Alpha Centauri triple-star system, about 4.37 light-years away. Sun 0.0000158 so it is 270,000 times further away

Some planets are made of gas True – they are called the gas giants.Astrology is the study of how the planets control your destiny.

True – it has absolutely no basis in science at all

We have summers and winters because of the tilt of the earth.

True – the Earth is tilted to 23o from it’s plane of orbits and is why we have seasons.

The Earth spins on its axis once a year. False – it spins on its axis once a day – that is the definition of a day

The Earth orbits the sun once a day. False – this is the definition of a yearOther stars have planets. True – about 4,000 extrasolar planets have been

discovered so far.Telescopes are put up mountains so that they are nearer to the stars.

False – they are on mountains so there is less atmosphere to get into the way of the view.

Solar system questions

1. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.2. Between Mars and Jupiter3. An object that orbits the sun, massive enough to be spherical and has cleared the neighbourhood4. Pluto has not cleared it’s neighbourhood5. Milky Way6.

I. Venus has an atmosphere that traps heat II. Jupiter

III. JupiterIV. Jupiter, Saturn, Uranus and Neptune. The rings are made up of billions of small particles, rock, dust

and ice.

Life cycle of stars

1 Gravity acting inwards, radiation outwards;

Stable since forces are balanced.

2 Light elements due to fusion

Heavy elements from supernova

3 Loss of mass = 0.7% of 2 g = 0.000014 kg

E = m c2 = 1.4 x 10–5 X (3 x 108)2 = 1.26 x 1012 J

4 a the larger the star, the shorter its lifetime

b white dwarf → black dwarf

c supernova → neutron star.

d supernova → black hole

5 E, C, A, F, B, D

Satellites and Orbits

1 A smaller celestial object orbiting a larger celestial object

2 Velocity has both magnitude and direction - the magnitude (speed) is staying the same but the direction is changing. A change in velocity is an acceleration

3

4 I geostationary satellite orbits once every 24 hours, GPS satellite orbits in half this time, the larger the orbit, the longer it takes so GPS satellite in lower orbit

II weather satellite takes less time to orbit than GPS satellite, the larger the orbit, the longer it takes so weather satellite in lower orbit than GPS satellite

5 36,000km

6 C=2πr

C = 2x3.14x(6400 + 15000)

C = 134,392km

v = 134,392km / (500mins x 60) = 4.5 km/s

Expanding universe

1. The observed frequency of waves emitted by a moving object appear changed.

2. When light is moving away from the observe it is shifted towards the red end of the spectrum

3. It is red-shifted – shifted towards the red end of the spectrum

4. It is expanding

5. a) Y, b) X

6. The light will be shifted towards the blue end of the spectrum.

7. There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. As there is nothing special about our location in space all objects are accelerating away from each other – the universe is expanding.

The beginning and the end

1 a Away from us, as the light is red shifted / shifted to the red end / longer wavelength end of the spectrum

b i They would be shifted further to the red end.

ii They would be shifted in the opposite direction / towards the blue end of the spectrum.

2 a How fast the galaxies are moving away from Earth based on their distance from Earth

b The further the galaxies are away from Earth, the faster they are moving, which suggests that the Universe is increasing in size

c i The gradient of the graph is speed / distance , which has units of s–1 so the inverse of that gives the time that the Universe has been expanding / age of the Universe.

ii

1000 km/s20 million light years gives a value for the gradient of 5.28 10–18 s–1 . The inverse of this

gives a value for the age of the Universe as 1.9 1017 s or 6 billion years

3 Any 6 from:

The CMBR is the echo of the explosion from the Big Bang (1) and has a wavelength / temperature (1) that has increased /decreased over time (1) as the Universe has expanded and cooled (1). If the Universe did start in a Big Bang at a certain / predicted time then the CMBR should be a particular value with a temperature of 2.7K (1), which is what was detected, suggesting that the Universe is about 13.7 billion years old (1). If the Universe was not this age then the value would be different, so the evidence fits with what was predicted

Glossary

Big Bang theory

the theory that the universe was created in a massive explosion (the Big Bang), and that the universe has been expanding ever since

black dwarf

a star that has faded out and gone cold

black hole

an object in space that has so much mass that nothing, not even light, can escape from its gravitational field

centripetal force

the resultant force towards the centre of a circle acting on an object moving in a circular path

cosmic microwave background radiation (CMBR)

electromagnetic radiation that has been travelling through space ever since it was created shortly after the Big Bang

dark matter

matter in a galaxy that cannot be seen. Its presence is deduced because galaxies would spin much faster if their stars were their only matter

main sequence

the main sequence is the life stage of a star during which it radiates energy because of fusion of hydrogen nuclei in its core

neutron star

the highly compressed core of a massive star that remains after a supernova explosion

protostar

the concentration of dust clouds and gas in space that forms a star

red giant

a star that has expanded and cooled, resulting in it becoming red and much larger and cooler than it was before

it expanded

red supergiant

a star much more massive than the Sun will swell out after the main sequence stage to become a red supergiant before it collapses

red-shift

increase in the wavelength of electromagnetic waves emitted by a star or galaxy due to its motion away from us.

The faster the speed of the star or galaxy, the greater the red-shift is

supernova

the explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses on to the core and rebounds

white dwarf

a star that has collapsed from the red giant stage to become much hotter and denser

Learning targets

Solar system HT?Know the 8 planets in orderKnow the sun is a starDefine a dwarf planetDefine natural and artificial satellitesThe life cycle of a starKnow the stages of a star’s life cycle for large and small starsKnow what nuclear fusion is and how it keeps a star stable Know how stars created the naturally occurring elementsKnow how the elements were distributed through the universeExplain how fusion processes lead to the formation of new elementsKnow gravity is the force that allows the planets and satellites to maintain their circular objectsOrbital motion, natural and artificial satellitesDescribe similarities and distinctions between the planets, their moons and artificial satellitesExplain the circular orbits that the force of gravity leads to changing velocity but unchanged speed

HT

Explain for a stable orbit the radius must change if the speed changes HTRed-shiftKnow that the universe is getting biggerKnow what red-shift isCan explain qualitatively that the red-shift shows that the galaxies are recedingKnow red-shift supports the Big Bang theoryKnow the universe began as a small region that was extremely hot and dense (known as the Big Bang theory)Explain the change of each galaxy speed with distance is evidence of an expanding universeKnow there is still much about the universe which is not understood e.g. dark mass and energy