Topic 8: Space Physics

Question 1

What are planets?

Answer 1

Large objects that orbit a star

Question 2

Example of a natural satellite

Answer 2

Moon

Question 3

What galaxy is our solar system in?

Answer 3

The Milky Way

Question 4

Describe the life cycle of a star up to and including its main sequence [6]

Answer 4

1. Star initially form from a cloud of dust and gas called a nebula
2. The force of gravity pulls the dust and gas together to form a protostar
3. The temperature rises as the star gets denser and more particles collide with each other
4. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
5. This gives out huge amounts of energy, which keeps the core of the star hot
6. The star then enters a long stable period where the outward pressure caused by nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards - main sequence

Question 5

Describe the life cycle of a star much larger than our sun, from its main sequence onwards [4]

Answer 5

1. When the star runs out of hydrogen to fuse, it will expand and cool, becoming a red super giant
2. It begins to glow brightly again and expands and contracts several times until it explodes in a supernova
3. The supernova throws dust and gas into space and leaves behind a very dense core called a neutron star
4. This will become a black hole if it is massive enough

Question 6

Describe the life cycle of a star like our sun, from its main sequence onwards [4]

Answer 6

1. When the star runs out of hydrogen to fuse, it will expand and cool, becoming a red giant
2. The star becomes unstable and ejects its outer layer of dust and gas
3. This leaves behind a hot, dense solid core - a white dwarf
4. As a white dwarf cools down, it emits less and less energy. When it no longer emits a significant amount, it is called a black dwarf

Question 7

Describe when various elements are made in a star’s life cycle [3]

Answer 7

1. A main sequence star only fuses hydrogen to make helium
2. In red giants or red super giants, nuclear fusion can form heavier elements up to iron in the periodic table
3. Elements heavier than iron are formed in supernovas

Question 8

Explain why the moon is technically accelerating in its orbit of the Earth [3]

Answer 8

1. The moon changes direction as it orbits the Earth
2. Therefore, its velocity is changing
3. Therefore, it must be accelerating

Question 9

If the distance between the Moon and the Earth was smaller, how would the orbital speed of the Moon compare to its current speed? [3]

Answer 9

1. Its orbital speed would increase
2. This is because the force due to gravity would be greater on the Moon as it is closer to the Earth
3. Therefore, to remain in stable orbit, the Moon’s instantaneous velocity would have to increase

Question 10

Describe the simple theory of red-shift [2]

Answer 10

1. When we look at light from most distant galaxies, we find the wavelengths has increased
2. The wavelengths are all longer than they should be - they’ve shifted towards the red end of the spectrum

Question 11

What does the idea of red-shift suggest?

Answer 11

That distant galaxies are moving away from us, and therefore the whole universe is expanding

Question 12

Red-shift

What is true of the most distance galaxies?

Answer 12

They are moving away the fastest

Question 13

Describe the Big Bang Theory [2]

Answer 13

1. Initially, all the matter in the universe occupied a very small space. It was very dense and therefore hot
2. Then it exploded - space started expanded and it still is

Question 14

What present day observations suggest that distant galaxies are moving faster and faster away from us?

Answer 14

Observations of supernovas from 1998