Space physics

IGCSE PHYSICS

Space physics

Overview

6. Space physics

6.1 Earth and the Solar System

• The Earth and time measurements,
• The solar system; Sun & Planets,
Distances and times, gravitational
forces.

• The Sun as a star,

• Stars,

• The Universe (and the red shift)

6.2 Stars and the Universe

The Earth, Moon and the Sun.

The Earth, Moon and the Sun.

The Earth's Axis​
The Earth is a rocky planet that;
1. Orbits the Sun once every 365 days (1 year)
2. Follows an approximately circular (elliptical) orbit
3. Completes one full rotation on its axis once every 24 hours (1 day),
4. Is tilted on its axis (a line through the north and south poles) at an angle of approximately 23.5°

Earth, moon and sun ideo link

Day and Night

• The Earth's rotation on its tilted axis creates day and night.

• Day is experienced by the half of the Earth's surface that is facing the Sun.

• Night is the other half of the Earth's surface, facing away from the Sun

Rising and Setting of the Sun

Rising and Setting of the Sun

• The Earth's rotation on its axis makes the Sun looks like it moves from east to west

  • At the equinoxes the Sun rises exactly in the east and sets exactly in the west  

  • Equinox (meaning 'equal night') is when day and night are approximately of equal length

Rising and Setting of the Sun

• However, the exact locations of where the Sun rises and sets changes throughout the seasons

   

• In the northern hemisphere (above the equator): 

  • In summer, the sun rises north of east and sets north of west

  • In winter, the sun rises south of east and sets south of west

Rising and Setting of the Sun

• The Sun is highest above the horizon at noon (12 pm)

• In the northern hemisphere, the daylight hours are longest up until roughly the 21st June

  • This day is known as the Summer Solstice and is where the Sun is at its highest point in the sky all year

• The daylight hours then decrease to their lowest around 21st December

  • This is known the Winter Solstice and is where the Sun is at its lowest point in the sky all year

The Earth's Orbit & Seasons

The Earth's Orbit

• The Earth orbits the Sun once every year, which is approximately 365 days.

• The combination of the orbiting of the Earth around the Sun and the Earth's tilt creates the seasons

Seasons in the Northern Hemisphere are caused by the tilt of the Earth

• Over parts B, C and D of the orbit, the northern hemisphere is tilted towards the Sun

  • This means daylight hours are more than hours of darkness

  • This is spring and summer

• The southern hemisphere is tilted away from the Sun

  • This means there are shorter days than night

  • This is autumn and winter

• Over parts F, G and H of the orbit, the northern hemisphere is tilted away from the Sun

  • The situations in both the northern and southern hemispheres are reversed

  • It is autumn and winter in the northern hemisphere, but at the same time it is spring and summer in the southern hemisphere

Seasons video link

• At C:

  • This is the summer solstice

  • The northern hemisphere has the longest day, whilst the southern hemisphere has its shortest day

• At G:

  • This is the winter solstice

  • The northern hemisphere has its shortest day, whilst the southern hemisphere has its longest day

• At A and D:

  • Night and day are equal in both hemispheres

  • These are the equinoxes

Countries at the Equator do not experience seasons because the Sun’s rays always hit them at the same angle. The seasonal differences are more apparent the further from the Equator you are. In the far north or south, seasons are so extreme that, in winter, the Sun is hardly seen and, in summer, it can be sunny at midnight.

The Moon

• The Moon is a satellite that orbits around the Earth

• It travels around the Earth in roughly a circular orbit once a month, which takes around 28 days

• The Moon revolves around its own axis in a month so always has the same side facing the Earth

  • We never see the hemisphere that is always facing away from Earth, although astronauts have orbited the Moon and satellites have photographed it

• The Moon shines with reflected light from the Sun, it does not produce its own light

The Moon

We always see the same side of the Moon as it rotates on its axis and orbits the Earth at the same rate

The phases of the Moon.
As the Moon orbits the Earth, the half of the Moon that faces the Sun will be lit up by the Sun. As the Moon moves, the shape of the light part, which can be seen from the Earth, changes. The outer circle of Moon diagrams shows how the Moon looks to an observer on Earth

Multiple Choice

When the Moon is directly between the Sun and the Earth, what phase would the Moon be in?

• 
  Full Moon

• 
  Half Moon

• New moon
• 
  Waxing Crescent

Our solar system is a small part of a galaxy called the Milky Way.

Our star (The Sun) is just one of
approximately 300 000 000 000 stars in our
galaxy. The whole solar system is too small
to see on this picture of the Milky Way.

There is thought to be a massive black hole
at the centre of the Milky Way.

The Universe is thought to have formed about 13.7 billion years ago.

The solar system formed around 4.6 billion years ago.

Space physics; orbital motions and satellites –

Our solar system

The solar system is any object that is bound by gravity to a Sun. All objects in

the solar system orbit The Sun.

Our solar system there is:
•one star – the Sun

•eight planets

•dwarf planets

•natural satellites called
moons that orbit planets.

Other objects in
The solar system include:
•Comets

•Asteroids

•Satellites

Dust, ice and rocks make up
the remaining mass.

Space physics; orbital motions and satellites –

Formation of the sun and solar system

(a) The universe contains ‘clumps’ of

dust and gas each called a nebula.

(b) Gravitational attraction pulls this

dust and gas together.

(c) Forming the Sun (a star).
(d) Fusion reactions lead to an

equilibrium between the
gravitational collapse of the star and
the expansion of a star due to fusion
energy.

(e) The remaining parts of the solar

system form from the remaining
dust and gas.

Space physics; orbital motions and satellites –

Stability of the sun

The Sun, like all stars, releases energy through nuclear fusion reactions in the

core.

Two isotopes of Hydrogen (Deuterium and
Tritium) are forced together under high
temperature and pressure. Nuclear fusion
occurs to form Helium and a neutron.
A tiny amount of mass is converted into a
large amount of energy, which is why stars
emit a lot of energy.

The heat produced in the fusion process makes the star
expand through thermal pressure.
Gravitational attraction is pulling the mass of the star
inwards.
In a stable star, thermal expansion and gravitational
attraction are equal so the star remains the same size.
This balance can change later in a star’s life when a great
increase in thermal pressure can cause it to expand.

Space physics; orbital motions and satellites –

Life cycle of a star

Stars go through a life cycle which is different for massive stars and smaller stars.

Stars about the
same size as the
Sun

Stars much
bigger than

the Sun

Nebula
(Cloud of
gas and

dust)

Protostar

Main sequence star

Red Giant

White dwarf

Black dwarf

Red super giant

Supernova

Neutron star

Black hole

Small stars
live a lot

longer than
massive stars
as they use up

their fuel

more slowly.

The Sun will be a
main sequence
star for 20 billion
years. Massive

stars can last less

than a million

years.

Space physics; orbital motions and satellites –

Stars and the elements

•Fusion processes in stars produce all of the naturally occurring elements.

•Elements heavier than iron are produced in a supernova.

•The explosion of a massive star (supernova) distributes the elements
throughout the universe.

How fusion processes lead to to the formation of new elements:
Stars begin with hydrogen as their “fuel”. Hydrogen nuclei join to becomes
helium during the fusion process. Further fusion processes continue to create
larger elements (as big as iron on the periodic table).
Elements bigger than iron are produced in a supernova. The supernovae
distribute elements throughout the Universe.

Space physics; orbital motions and satellites –

Orbits and speed

Sun

Gravity

Gravity pulls the Earth (and other
planets) towards the sun. The planet
is effectively “falling” towards the sun
but is travelling fast enough so that it
constantly misses falling into the sun.

This is like a cannon firing a cannonball at
just the right speed so it does not escape
into space or fall down to Earth.
This is how planets, moons and artificial
satellites remain in orbit around larger
objects in space.

The force of gravity increases the closer an object orbits. To avoid being pulled

into the sun, a planet must be travelling faster, the closer it is to the sun.

This is why Mercury’s orbit of the sun takes 3 Earth months whereas it takes

Neptune 165 Earth years to orbit the sun.

Space physics; orbital motions and satellites –

Orbits and speed (HT)

In a perfectly circular orbit, a body will travel at constant speed to maintain its
orbital distance.
However, gravity is constantly changing the direction of the body. As velocity
depends on speed and direction, the velocity is constantly changing even
though speed remains the same.
This applies to planets, moons and satellites.

Planets velocity is in a straight line.
Gravity causes body to change
direction so velocity must be
changing

QuestionIT!

Solar system: stability of
orbital motions; satellites
(physics only)

• Our solar system
• The life cycle of a star
• Orbital motion, natural and

artificial satellites

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

1. Name the star in our solar system.

2. How many planets in our solar system?

3. What is the difference between a moon and a dwarf planet?

4. What do we call the natural satellites in the solar system?

5. Name the galaxy our solar system is part of.

6. How was the sun formed, and what caused this to happen?

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

7. List the major bodies found in the solar system.

8. What is a nebula?

9. What determines the life cycle a star will take?

10. Describe the lifecycle of a star the size of the sun.

11. Describe the lifecycle of a star more massive than the sun.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

12. What processes produce all of the naturally occurring elements?

13. Where are elements heavier than iron produced?

14. How are these elements distributed throughout the universe?

15. What force enables planets and satellites to maintain their circular

orbits?

Solar system: stability of orbital motions; satellites (physics only)

– QuestionIT

16. Main sequence stars are stable despite opposing forces acting on

the star. Describe forces A and B.

17. The international space station takes 92 mins to orbit the Earth.

The Moon takes 27.3 days to orbit the Earth. Explain why these
orbital times are different.

A

B

Solar system: stability of orbital motions; satellites

physics only) (HT) – QuestionIT

18. The diagram shows a satellite orbiting the Earth.

Explain how the Earth’s gravity can result in the
satellites velocity changing but not its speed.

19. Explain why satellites in a polar orbit must travel at much higher

speeds than a satellite in a geostationary orbit.

AnswerIT!

Changes of state and
the particle model

•

Density of materials

•

Changes of state

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

1. Name the star in our solar system.

The Sun.

2. How many planets in our solar system?

8

3. What is the difference between a moon and a dwarf planet?

Dwarf planets orbit the sun; moons orbit planets.

4. What do we call the natural satellites in the solar system?

Moons.

5. Name the galaxy our solar system is part of.

The Milky Way.

6. How was the sun formed, and what caused this to happen?

From a cloud of dust and gas (nebula); pulled together by
gravitational attraction; causing fusion reactions.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

7. List the major bodies found in the solar system.

Star, planets, dwarf planets, moons, asteroids, comets.

8. What is a nebula?

Could of dust and gas.

9. What determines the life cycle a star will take?

The size of the star.

10. Describe the lifecycle of a star the size of the sun.

Cloud of gas and dust, protostar, main sequence star, red giant,
white dwarf, black dwarf.

11. Describe the lifecycle of a star more massive than the sun.

Cloud of gas and dust, protostar, main sequence star, red super
giant, supernova, neutron star or black hole.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

12. What processes produce all of the naturally occurring elements?

Fusion.

13. Where are elements heavier than iron produced?

Supernova.

14. How are these elements distributed throughout the universe?

Explosion of massive star (supernova).

15. What force enables planets and satellites to maintain their circular

orbits?
Gravity.

Solar system: stability of orbital motions; satellites (physics only)

– QuestionIT

16. Main sequence stars are stable despite opposing forces acting on

the star. Describe forces A and B.
A – gravitational attraction
B – thermal expansion

16. The international space station takes 92 mins to orbit the Earth.

The Moon takes 27.3 days to orbit the Earth. Explain why these
orbital times are different.
Moon orbits at a much greater distance than the ISS; it is much
further away from the Earth.
The further from the Earth the lower the gravitational attraction
So The Moon travels slower and it takes much longer to orbit
the Earth.

A

B

Solar system: stability of orbital motions; satellites

physics only) (HT) – QuestionIT

18. The diagram shows a satellite orbiting the Earth.

Explain how the Earth’s gravity can result in the
satellites velocity changing but not its speed.
In a circular orbit the speed of the satellite
remains constant. Velocity is a vector so has
size AND direction.
As the direction is changing, the velocity
must be changing.

19. Explain why satellites in a polar orbit must travel at much higher

speeds than a satellite in a geostationary orbit.
Polar satellite are in a much lower orbit than
geostationary satellites.
In a lower orbit, gravity has a much stronger
influence so the polar satellite must travel much
faster to avoid being pulled down to Earth.

LearnIT!
KnowIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift

There are billions of galaxies in the Universe. We can see them because the

stars within them give off light which travels to Earth.

Nearby star

Distant galaxy

Light from a nearby star appears white as the wavelength of light emitted
covers the whole visible spectrum.
The light we receive from a distant galaxy has had its wavelength increased.
As longer wavelengths of light are the red end of the spectrum, the light
appears redder than from the nearby star – this is called RED SHIFT.

Red shift happens because the galaxy is
moving away from us at high speed, causing
the wavelengths of light to be stretched.

Red shift

Light emitted by a hot object

produces a continuous spectrum.
When light is emitted by a star, the
light has to travel through the gases

which make up the star.

These gases absorb specific

wavelengths of light, leaving black

lines in the spectrum.

Absorption spectra from stars in every galaxy would look the same if all the
galaxies were a fixed distance from the Earth. Galaxies have different amounts of
red shift which means they are moving away from us at different speeds.

The faster a galaxy is moving, the further away it is.

Spectrum from a star in our galaxy – no red shift
Spectrum from a star in another galaxy – some
red shift
Spectrum from a distant galaxy – a lot of red
shift

Red shift

Summary

• Red light has a longer wavelength than blue light.

• Most distant galaxies show an increase in wavelength of light.

• The further away the galaxies the faster they are moving and

the bigger the increase in wavelength.

• This effect is called the RED-SHIFT.

• The observed red-shift provides evidence that the universe is

expanding and supports the Big Bang theory.

Big Bang theory

Like a balloon expanding, all galaxies are moving away from each other and from
a point of origin. Only the fastest moving galaxies would be on the surface of this
model. Slower moving galaxies would be on the inside but still moving away from
the centre. These observations have provided evidence of an expanding Universe.

Galaxies

Universe
expands
over time

Red shift measurements of many galaxies have given evidence that all
galaxies are moving away from a single point of origin at different speeds.
This has led to the Big Bang theory that the Universe expanded from a single
point of matter around 13.7 billion years ago.

Understanding the Universe

Over the last century, much has been discovered about our Universe:

• The age of the Universe.
• The Universe is more than just our galaxy.
• The size of the Universe.
• There are probably billions of other planets beyond our Solar System.
• The Universe is expanding.
• Cosmic microwave background radiation supporting the Big Bang theory.

However, there is still much we do not yet understand about the Universe.

• Dark matter and dark energy – continued expansion and acceleration of

the Universe suggests there must be a lot more matter and energy than
we can see. This is described as dark matter/energy that we have yet to
find.

• Fate of the Universe. Is the Universe going to continue forever or

collapse back to a point and start again?

• Is our Universe just one of a series of multiverses?
• Does life exist anywhere else in the Universe?

QuestionIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift and Big Bang theory – QuestionIT

1. Which colour of light has the longest wavelength?

2.

The diagram shows the spectrum of light from a star in our galaxy.

Copy the second box by adding the spectra you would expect from a
star in a distant galaxy.

3. The light reaching Earth from distant galaxies exhibits red shift.

Explain why red shift occurs.

Red

Blue

Blue

Red

Red shift and Big Bang theory – QuestionIT

4.

Galaxy A

Galaxy B

If galaxy A has a much bigger red shift than galaxy B, what does this
tell you about galaxy A?

5.

Which theory about the origin of the Universe does red shift of
galaxies support?

6.

Approximately how many years ago did the Universe begin? (Circle the
correct answer)

14 million

14 billion

14 trillion

Red shift and Big Bang theory – QuestionIT

7. What does the diagram suggest is happening to the Universe over

time?

8. Describe the current theory of how the Universe began.

9.

Atoms are only thought to make up about 5% of the known Universe.
What do scientists think the remaining 95% is made up of?

10. The most distant galaxies in the Universe are thought to be:

(tick the correct box)

The biggest galaxies

Accelerating

Slowing down

The coldest

AnswerIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift and Big Bang theory – AnswerIT

1.

Which colour of light has the longest wavelength?

2.

The diagram shows the spectrum of light from a star in our galaxy.

Copy the second box by adding the spectra you would expect from a
star in a distant galaxy.

3. The light reaching Earth from distant galaxies exhibits red shift.

Explain why red shift occurs.
Galaxy is moving away at high speed
Light waves from the galaxy are being stretched to longer wavelengths.
Longer wavelengths of light are found at the red end of the spectrum.
This shift of wavelength is called red shift.

Red

Blue

Blue

Red

Red

Red shift and Big Bang theory – AnswerIT

4.

Galaxy A

Galaxy B

If galaxy A has a much bigger red shift than galaxy B, what does this
tell you about galaxy A?
It is travelling away at a higher speed. It is further away.

5.

Which theory about the origin of the Universe does red shift of
galaxies support?
Big Bang theory.

6.

Approximately how many years ago did the Universe begin? (Circle the
correct answer)

14 million

14 billion

14 trillion

Red shift and Big Bang theory – QuestionIT

7. What does the diagram suggest is happening to the Universe over

time?

It is expanding.

8. Describe the current theory of how the Universe began.

Started as a small region that was very hot and dense.
Big Bang caused it to rapidly expand.

9.

Atoms are only thought to make up about 5% of the known Universe.
What do scientists think the remaining 95% is made up of?
Dark matter and dark energy.

10. The most distant galaxies in the Universe are thought to be:

(tick the correct box)

The biggest galaxies

Accelerating

Slowing down

The coldest



Space physics; orbital motions and satellites –

Our solar system

The solar system is any object that is bound by gravity to a Sun. All objects in

the solar system orbit The Sun.

Our solar system there is:
•one star – the Sun

•eight planets

•dwarf planets

•natural satellites called
moons that orbit planets.

Other objects in
The solar system include:
•Comets

•Asteroids

•Satellites

Dust, ice and rocks make up
the remaining mass.

Space physics; orbital motions and satellites –

Formation of the sun and solar system

(a) The universe contains ‘clumps’ of

dust and gas each called a nebula.

(b) Gravitational attraction pulls this

dust and gas together.

(c) Forming the Sun (a star).
(d) Fusion reactions lead to an

equilibrium between the
gravitational collapse of the star and
the expansion of a star due to fusion
energy.

(e) The remaining parts of the solar

system form from the remaining
dust and gas.

Space physics; orbital motions and satellites –

Stability of the sun

The Sun, like all stars, releases energy through nuclear fusion reactions in the

core.

Two isotopes of Hydrogen (Deuterium and
Tritium) are forced together under high
temperature and pressure. Nuclear fusion
occurs to form Helium and a neutron.
A tiny amount of mass is converted into a
large amount of energy, which is why stars
emit a lot of energy.

The heat produced in the fusion process makes the star
expand through thermal pressure.
Gravitational attraction is pulling the mass of the star
inwards.
In a stable star, thermal expansion and gravitational
attraction are equal so the star remains the same size.
This balance can change later in a star’s life when a great
increase in thermal pressure can cause it to expand.

Space physics; orbital motions and satellites –

Life cycle of a star

Stars go through a life cycle which is different for massive stars and smaller stars.

Stars about the
same size as the
Sun

Stars much
bigger than

the Sun

Nebula
(Cloud of
gas and

dust)

Protostar

Main sequence star

Red Giant

White dwarf

Black dwarf

Red super giant

Supernova

Neutron star

Black hole

Small stars
live a lot

longer than
massive stars
as they use up

their fuel

more slowly.

The Sun will be a
main sequence
star for 20 billion
years. Massive

stars can last less

than a million

years.

Space physics; orbital motions and satellites –

Stars and the elements

•Fusion processes in stars produce all of the naturally occurring elements.

•Elements heavier than iron are produced in a supernova.

•The explosion of a massive star (supernova) distributes the elements
throughout the universe.

How fusion processes lead to to the formation of new elements:
Stars begin with hydrogen as their “fuel”. Hydrogen nuclei join to becomes
helium during the fusion process. Further fusion processes continue to create
larger elements (as big as iron on the periodic table).
Elements bigger than iron are produced in a supernova. The supernovae
distribute elements throughout the Universe.

Space physics; orbital motions and satellites –

Orbits and speed

Sun

Gravity

Gravity pulls the Earth (and other
planets) towards the sun. The planet
is effectively “falling” towards the sun
but is travelling fast enough so that it
constantly misses falling into the sun.

This is like a cannon firing a cannonball at
just the right speed so it does not escape
into space or fall down to Earth.
This is how planets, moons and artificial
satellites remain in orbit around larger
objects in space.

The force of gravity increases the closer an object orbits. To avoid being pulled

into the sun, a planet must be travelling faster, the closer it is to the sun.

This is why Mercury’s orbit of the sun takes 3 Earth months whereas it takes

Neptune 165 Earth years to orbit the sun.

Space physics; orbital motions and satellites –

Orbits and speed (HT)

In a perfectly circular orbit, a body will travel at constant speed to maintain its
orbital distance.
However, gravity is constantly changing the direction of the body. As velocity
depends on speed and direction, the velocity is constantly changing even
though speed remains the same.
This applies to planets, moons and satellites.

Planets velocity is in a straight line.
Gravity causes body to change
direction so velocity must be
changing

QuestionIT!

Solar system: stability of
orbital motions; satellites
(physics only)

• Our solar system
• The life cycle of a star
• Orbital motion, natural and

artificial satellites

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

1. Name the star in our solar system.

2. How many planets in our solar system?

3. What is the difference between a moon and a dwarf planet?

4. What do we call the natural satellites in the solar system?

5. Name the galaxy our solar system is part of.

6. How was the sun formed, and what caused this to happen?

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

7. List the major bodies found in the solar system.

8. What is a nebula?

9. What determines the life cycle a star will take?

10. Describe the lifecycle of a star the size of the sun.

11. Describe the lifecycle of a star more massive than the sun.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

12. What processes produce all of the naturally occurring elements?

13. Where are elements heavier than iron produced?

14. How are these elements distributed throughout the universe?

15. What force enables planets and satellites to maintain their circular

orbits?

Solar system: stability of orbital motions; satellites (physics only)

– QuestionIT

16. Main sequence stars are stable despite opposing forces acting on

the star. Describe forces A and B.

17. The international space station takes 92 mins to orbit the Earth.

The Moon takes 27.3 days to orbit the Earth. Explain why these
orbital times are different.

A

B

Solar system: stability of orbital motions; satellites

physics only) (HT) – QuestionIT

18. The diagram shows a satellite orbiting the Earth.

Explain how the Earth’s gravity can result in the
satellites velocity changing but not its speed.

19. Explain why satellites in a polar orbit must travel at much higher

speeds than a satellite in a geostationary orbit.

AnswerIT!

Changes of state and
the particle model

•

Density of materials

•

Changes of state

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

1. Name the star in our solar system.

The Sun.

2. How many planets in our solar system?

8

3. What is the difference between a moon and a dwarf planet?

Dwarf planets orbit the sun; moons orbit planets.

4. What do we call the natural satellites in the solar system?

Moons.

5. Name the galaxy our solar system is part of.

The Milky Way.

6. How was the sun formed, and what caused this to happen?

From a cloud of dust and gas (nebula); pulled together by
gravitational attraction; causing fusion reactions.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

7. List the major bodies found in the solar system.

Star, planets, dwarf planets, moons, asteroids, comets.

8. What is a nebula?

Could of dust and gas.

9. What determines the life cycle a star will take?

The size of the star.

10. Describe the lifecycle of a star the size of the sun.

Cloud of gas and dust, protostar, main sequence star, red giant,
white dwarf, black dwarf.

11. Describe the lifecycle of a star more massive than the sun.

Cloud of gas and dust, protostar, main sequence star, red super
giant, supernova, neutron star or black hole.

Solar system: stability of orbital motions; satellites

(physics only) – QuestionIT

12. What processes produce all of the naturally occurring elements?

Fusion.

13. Where are elements heavier than iron produced?

Supernova.

14. How are these elements distributed throughout the universe?

Explosion of massive star (supernova).

15. What force enables planets and satellites to maintain their circular

orbits?
Gravity.

Solar system: stability of orbital motions; satellites (physics only)

– QuestionIT

16. Main sequence stars are stable despite opposing forces acting on

the star. Describe forces A and B.
A – gravitational attraction
B – thermal expansion

16. The international space station takes 92 mins to orbit the Earth.

The Moon takes 27.3 days to orbit the Earth. Explain why these
orbital times are different.
Moon orbits at a much greater distance than the ISS; it is much
further away from the Earth.
The further from the Earth the lower the gravitational attraction
So The Moon travels slower and it takes much longer to orbit
the Earth.

A

B

Solar system: stability of orbital motions; satellites

physics only) (HT) – QuestionIT

18. The diagram shows a satellite orbiting the Earth.

Explain how the Earth’s gravity can result in the
satellites velocity changing but not its speed.
In a circular orbit the speed of the satellite
remains constant. Velocity is a vector so has
size AND direction.
As the direction is changing, the velocity
must be changing.

19. Explain why satellites in a polar orbit must travel at much higher

speeds than a satellite in a geostationary orbit.
Polar satellite are in a much lower orbit than
geostationary satellites.
In a lower orbit, gravity has a much stronger
influence so the polar satellite must travel much
faster to avoid being pulled down to Earth.

LearnIT!
KnowIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift

There are billions of galaxies in the Universe. We can see them because the

stars within them give off light which travels to Earth.

Nearby star

Distant galaxy

Light from a nearby star appears white as the wavelength of light emitted
covers the whole visible spectrum.
The light we receive from a distant galaxy has had its wavelength increased.
As longer wavelengths of light are the red end of the spectrum, the light
appears redder than from the nearby star – this is called RED SHIFT.

Red shift happens because the galaxy is
moving away from us at high speed, causing
the wavelengths of light to be stretched.

Red shift

Light emitted by a hot object

produces a continuous spectrum.
When light is emitted by a star, the
light has to travel through the gases

which make up the star.

These gases absorb specific

wavelengths of light, leaving black

lines in the spectrum.

Absorption spectra from stars in every galaxy would look the same if all the
galaxies were a fixed distance from the Earth. Galaxies have different amounts of
red shift which means they are moving away from us at different speeds.

The faster a galaxy is moving, the further away it is.

Spectrum from a star in our galaxy – no red shift
Spectrum from a star in another galaxy – some
red shift
Spectrum from a distant galaxy – a lot of red
shift

Red shift

Summary

• Red light has a longer wavelength than blue light.

• Most distant galaxies show an increase in wavelength of light.

• The further away the galaxies the faster they are moving and

the bigger the increase in wavelength.

• This effect is called the RED-SHIFT.

• The observed red-shift provides evidence that the universe is

expanding and supports the Big Bang theory.

Big Bang theory

Like a balloon expanding, all galaxies are moving away from each other and from
a point of origin. Only the fastest moving galaxies would be on the surface of this
model. Slower moving galaxies would be on the inside but still moving away from
the centre. These observations have provided evidence of an expanding Universe.

Galaxies

Universe
expands
over time

Red shift measurements of many galaxies have given evidence that all
galaxies are moving away from a single point of origin at different speeds.
This has led to the Big Bang theory that the Universe expanded from a single
point of matter around 13.7 billion years ago.

Understanding the Universe

Over the last century, much has been discovered about our Universe:

• The age of the Universe.
• The Universe is more than just our galaxy.
• The size of the Universe.
• There are probably billions of other planets beyond our Solar System.
• The Universe is expanding.
• Cosmic microwave background radiation supporting the Big Bang theory.

However, there is still much we do not yet understand about the Universe.

• Dark matter and dark energy – continued expansion and acceleration of

the Universe suggests there must be a lot more matter and energy than
we can see. This is described as dark matter/energy that we have yet to
find.

• Fate of the Universe. Is the Universe going to continue forever or

collapse back to a point and start again?

• Is our Universe just one of a series of multiverses?
• Does life exist anywhere else in the Universe?

QuestionIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift and Big Bang theory – QuestionIT

1. Which colour of light has the longest wavelength?

2.

The diagram shows the spectrum of light from a star in our galaxy.

Copy the second box by adding the spectra you would expect from a
star in a distant galaxy.

3. The light reaching Earth from distant galaxies exhibits red shift.

Explain why red shift occurs.

Red

Blue

Blue

Red

Red shift and Big Bang theory – QuestionIT

4.

Galaxy A

Galaxy B

If galaxy A has a much bigger red shift than galaxy B, what does this
tell you about galaxy A?

5.

Which theory about the origin of the Universe does red shift of
galaxies support?

6.

Approximately how many years ago did the Universe begin? (Circle the
correct answer)

14 million

14 billion

14 trillion

Red shift and Big Bang theory – QuestionIT

7. What does the diagram suggest is happening to the Universe over

time?

8. Describe the current theory of how the Universe began.

9.

Atoms are only thought to make up about 5% of the known Universe.
What do scientists think the remaining 95% is made up of?

10. The most distant galaxies in the Universe are thought to be:

(tick the correct box)

The biggest galaxies

Accelerating

Slowing down

The coldest

AnswerIT!

Red shift (physics only)

• Red shift
• Big bang theory

Red shift and Big Bang theory – AnswerIT

1.

Which colour of light has the longest wavelength?

2.

The diagram shows the spectrum of light from a star in our galaxy.

Copy the second box by adding the spectra you would expect from a
star in a distant galaxy.

3. The light reaching Earth from distant galaxies exhibits red shift.

Explain why red shift occurs.
Galaxy is moving away at high speed
Light waves from the galaxy are being stretched to longer wavelengths.
Longer wavelengths of light are found at the red end of the spectrum.
This shift of wavelength is called red shift.

Red

Blue

Blue

Red

Red

Red shift and Big Bang theory – AnswerIT

4.

Galaxy A

Galaxy B

If galaxy A has a much bigger red shift than galaxy B, what does this
tell you about galaxy A?
It is travelling away at a higher speed. It is further away.

5.

Which theory about the origin of the Universe does red shift of
galaxies support?
Big Bang theory.

6.

Approximately how many years ago did the Universe begin? (Circle the
correct answer)

14 million

14 billion

14 trillion

Red shift and Big Bang theory – QuestionIT

7. What does the diagram suggest is happening to the Universe over

time?

It is expanding.

8. Describe the current theory of how the Universe began.

Started as a small region that was very hot and dense.
Big Bang caused it to rapidly expand.

9.

Atoms are only thought to make up about 5% of the known Universe.
What do scientists think the remaining 95% is made up of?
Dark matter and dark energy.

10. The most distant galaxies in the Universe are thought to be:

(tick the correct box)

The biggest galaxies

Accelerating

Slowing down

The coldest

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