1. Astronomy 2016 EdExcel GCSE Physics Topic 7 W Richards
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Astronomy
2016 EdExcel GCSE Physics
Topic 7
W Richards
The Weald School

2. Note that this force goes both ways – the Earth is attracted to us.
Gravity
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Gravity is an attractive force that affects anything with mass:
Note that this force goes both ways – the Earth is attracted to us.

3. Weight vs. Mass
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Earth’s Gravitational Field Strength is 10N/kg. In other words, a 1kg mass is pulled downwards by a force of 10N. W g M
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
What is the weight on Earth of a book with mass 2kg?
What is the weight on Earth of an apple with mass 100g?
Lee weighs 700N on the Earth. What is his mass?
On the moon the gravitational field strength is 1.6N/kg. What will Lee weigh if he stands on the moon?
20N 1N
70kg
112N

4. Gravity on different planets and the moon:
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Jupiter: g = 25N/Kg
Earth – gravitational field strength = 10N/Kg
The moon: g = 1.6N/Kg

5. The eight planets of our Solar System
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Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
As well as the eight planets, the solar system is also made up of asteroids, dwarf planets, comets and moons

6. Our understanding of the solar system
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Ptolemy, AD
Up until the 16th Century people believed that the Earth was the centre of the universe – this is called the “Geocentric model” and I made a model of the universe based on it.
Copernicus,
I published my “On the revolutions of the celestial spheres” just before my death and showed that the Earth and other planets orbit around the sun – the “Heliocentric model”.

7. Evidence for the Heliocentric Model
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Galileo,
I helped develop the modern telescope and made measurements with it that proved that the Copernican model of the solar system was correct.
Jupiter and its moons, as seen through a telescope
The orbits of these moons

8. Asteroids
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An “asteroid belt” lies between Mars and Jupiter and orbits the sun. But what is an asteroid?

9. Notice how the tail always points away from the sun!
Comets
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Comets are balls of dust and frozen gas. They have very elliptical orbits:
Notice how the tail always points away from the sun!

10. The Solar System summarised
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What makes up our solar system? Complete the following mind map with what you now about each object:
The solar system

11. The Earth’s Orbit
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Gravity keeps us in orbit around the sun. How long does this orbit take?
Ellipse

12. Circular Motion recap 1) Is this car travelling at constant speed?
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1) Is this car travelling at constant speed?
2) Is this car travelling at constant velocity?

13. The Moon’s Orbit
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Gravity also keeps the moon (a natural satellite) in orbit around us. How long does this take?
Does the moon travel at constant speed?
Does it travel at constant velocity?

14. Satellite orbits
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Gravity also keeps artificial satellites in orbit around us.
Q. What would have to happen to the satellite’s speed if it moved closer to the Earth?
A. As the orbital radius INCREASES the speed of the satellite will DECREASE.

15. The formation of the universe
Stephen Hawking
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The formation of the universe
There are two main theories about how the universe started:
The “Steady State” theory
This theory states that the universe has always existed as it does now and hasn’t changed. The trouble is that the night sky would be completely lit up because of the billions of stars, but it’s not, so…
The “Big Bang” theory
This theory states that the universe started off with an explosion and everything has been moving away ever since. There are two main pieces of evidence for this: background microwave radiation and red shift.

16. How did the universe begin?
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How did the universe begin?
The Big Bang Theory suggests that the universe began from a very small region that was very hot and dense, and then…

17. How did the universe begin?
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How did the universe begin?

18. Evidence for the Big Bang Theory
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Source of light
“Spectra”

19. If you pass the light through a gas something different is seen…
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If you pass the light through a gas something different is seen…
helium
Some wavelengths of light are absorbed by the gas – an “absorption spectrum”.

20. Before helium helium After
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If the light source is moving away the absorption spectra look a little different…
helium
Before
helium
After

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The absorption lines have all been “shifted” towards the longer wavelength end (red end)…
Before
This is called red shift. The faster the light source moves the further its light will be “shifted”
After
A similar effect happens with sound – this is called “The Doppler Effect”

22. Red Shift simplified
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Basically, if I walk towards you I’ll look slightly more blue. Then, if I walk away from you, I’ll look slightly more red!!
Let’s try it…

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25. This is the BIG BANG theory
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Light from different stars and from the edge of the universe also shows this “red-shift”. This suggests that everything in the universe is moving away from a single point.
This is the BIG BANG theory

26. Red shift summary
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Light from other galaxies has a longer _________ than expected. This shows that these galaxies are moving ____ from us very quickly. This effect is seen to a greater extent in galaxies that are _______ away from us. This indicates that the further away the galaxy is, the ______ it is moving.
Words to use – faster, away, big bang, billion, wavelength, further, supernovae
This evidence seems to suggest that everything in the universe is moving away from a single point, and that this process started around 14 _____ years ago. This is the ____ ________ Theory. Observations of ________ from 1998 onwards have suggested that distant galaxies are receding even faster.

27. Cosmic Microwave Background Radiation
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Further evidence of the Big Bang theory is Cosmic Microwave Background Radiation (CMBR) – this radiation comes from the Big Bang and fills the _________.
Basically, at the start of the universe, radiation was hot and had high _______. As time went on the ________and energy of this radiation dropped which turned it into ________. This “background microwave _______” is all over the universe.
Words – microwaves, frequency, temperature, universe, radiation

28. Big Bang Theory vs Steady State
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Some scientists have explained that red shift can actually be used to support the Steady State Theory As red shift may be a result of matter being created in spaces as the universe expands and contracts.
Stephen Hawking,
However, the discovery of CMBR was the final nail in the coffin for the Steady State theory. So, the Big Bang theory is now the widely accepted theory of how the universe began as there is more evidence for it.

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The Life Cycle of a Star

30. Stage 1: Nebulae A nebulae is a collection of dust, gas and rock.
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A nebulae is a collection of dust, gas and rock.
Some examples of nebulae…

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Dark nebula

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Emission nebula

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Reflection nebula

34. (This nebula is smaller and will only form a planet)
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Planetary nebula
(This nebula is smaller and will only form a planet)

35. Stage 2: Protostar Gravity will slowly pull these particles together…
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Gravity will slowly pull these particles together…
As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed

36. Words – heavier, balanced, hydrogen, nuclear, fusion
Stage 3: Main Sequence
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In a main sequence star the forces of attraction pulling the particles inwards are _________ by thermal expansion forces due to nuclear ______ reactions and the high temperature.
Stars are basically ________ reactors that use _______ as a fuel. During its main sequence a star will release energy by converting hydrogen and helium (light elements) into _________ elements and this is why the universe now contains a number of heavier elements.
Our sun is an example of a main sequence star – it’s in the middle of a 10 billion year life span
Words – heavier, balanced, hydrogen, nuclear, fusion

37. Stage 4: Red Giant
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Eventually the hydrogen and helium will run out. When this happens the star will become colder and redder and start to swell…
If the star is relatively small (like our sun) the star will become a RED GIANT
If the star is big (at least 4 times the size of our sun) it will become a RED SUPERGIANT

38. Stage 5: The Death
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What happens at this point depends on the size of the star…
1) For SMALL stars the red giant will collapse under its own gravity and form a very dense white dwarf:
Red giant
White dwarf
Black dwarf

39. This explosion is called a SUPERNOVA
Stage 5: The Death
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2) If the star was a RED SUPERGIANT it will shrink and then EXPLODE, releasing massive amounts of energy, dust and gas.
Before
After
This explosion is called a SUPERNOVA

40. Stage 5: The Death
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The dust and gas on the outside of the supernova are thrown away by the explosion and the remaining core turns into a NEUTRON STAR.
If the star is big enough it could become a BLACK HOLE instead.

41. Stage 6: Second generation stars
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The dust and gas thrown out by a supernova can be used to form a new star…
Our sun is believed to be a “______ ______ star” – this is because it contains some __________ elements along with hydrogen and ________. These heavier elements would have been produced by a ____________ and thrown out when the star exploded. These heavier elements are also found on planets, indicating that they might have been made from remains of previous _______ as well.
Words – helium, heavier, second generation, stars, supernova

42. The Life Cycle of a Star summary
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SMALL
stars
Protostar
BIG
stars
Main sequence
Red giant
Red super giant
White dwarf
Supernova
Black dwarf
Neutron star
Black hole
Basically, it all depends on the size of the star!

43. Observing the Universe
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Observing the Universe

44. Observing the Universe
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Consider different types of telescope:
Ground-based telescopes
Space-based telescopes
What are the advantages and disadvantages of each?

45. Benefits of observing above the atmosphere
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Clearly, ground-based telescopes are a problem because of a number of things:
The amount of _____ absorbed by the __________
Bad _______
Light is refracted, diffracted and _______ by the atmosphere (causing stars to “twinkle”)
Light ______from nearby cities
The solution is to put telescopes in space or build them high up on a mountain.
Words – pollution, weather, light, atmosphere, scattered