Space Physics (8)

Question 1

What is the life cycle of a star up until the main sequence

Answer 1

1) Stars initially form from a cloud of dust and gas called a nebula
2) Force of gravity pulls the dust and gas together to form a protostar, the temp rises as the star gets denser and more particles collide with each other. When he temp get’s high enough, hydrogen nuclei undergo nuclear fission to form helium nuclei. This gives out huge amounts of energy, which keeps the core of the star hot.
3) The star enters a long stable period where the outward pressure caused by the nuclear fusion that tries to expand the star balances the force of gravity pulling everything inwards. In this stable period its called a main sequence star and it typically lasts several billion years (like the sun)

Question 2

What happens to red giant

Answer 2

1) When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant
2) When all the nuclear reactions are over, a small star like the Sun may begin to contract under the pull of gravity. In this instance, the star becomes a white dwarf which fades and changes colour as it cools
3) 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 3

What happens to red super giants

Answer 3

1) A larger star with more mass will go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova, An exploding supernova throws hot gas into space
2) Depending on the mass at the start of its life, a supernova will leave behind either a neutron star or a black hole.

Question 4

What is the sun

Answer 4

• The Sun is the largest object in the Solar System. The Sun’s huge gravitational field keeps many other objects - planets, dwarf planets, asteroids and comets - in orbit around it

Question 5

What are planets

Answer 5

• These are large objects that orbit a star, they have to be large enough to have “cleared their neighbourhoods” (this means that their gravity is strong enough to have pulled in any nearby objects apart from their natural satellites

Question 6

What is a satellite

Answer 6

Body that orbits a planet. For example, the Moon is a natural satellite of the Earth but communication satellites are artificial satellites of the Earth

Question 7

How does orbit work

Answer 7

• The planets move around the sun in almost circular orbits
• if an object is travelling in a circle it is constantly changing direction, which means it is constantly accelerating
• This means it is constantly changing velocity (but not changing speed)
• For an object to accelerate, there must be a force acting on it, this force is directed towards the centre of the circle
• This force would cause the object to just fall towards whatever it was orbiting, but as the object is already moving, it just causes it to change it’s direction
• The object keeps accelerating towards what it’s orbiting, but the instantaneous velocity (which is at a right angle to the acceleration) keeps it travelling in a circle

Question 8

How does the gravitational force affect the orbit

Answer 8

• the closer you get to a star or planet, the stronger the gravitational force is
• the stronger the force, the faster the orbiting object needs to travel to remain in orbit
• for an object in a stable orbit, if the speed of the object changes the size (radius) of it’s orbit must do so too. Faster moving objects will move on in a stable orbit with a smaller radius than slower moving ones

Question 9

What is red shift

Answer 9

• The change in wavelength of light from a distant star moving away from Earth

Question 10

What is the big bang theory

Answer 10

• the theory that all the matter in the universe occupied a very small place
• Then it ‘exploded’ - space started expanding, and the expansion is still going