What is a nebula?
a cloud of dust and gas
What does the attractive force of gravity do to the nebula?
pull the dust and gas together to form a protostar
What does the force of gravity then do to the protostar?
squeezes the protostar making it more dense which raises the temperature
- once the temperature and pressure are high enough, hydrogen nuclei begin to fuse together to form helium nuclei in nuclear fusion
- releases large amounts of energy which keeps the core of the star hot
What is a main sequence star?
the long stable period within a star’s lifetime where the outward pressure (caused by nuclear fusion) is equal to the inward pressure (caused by gravity)
What happens when the star starts to run out of hydrogen?
unable to do nuclear fusion so the outward pressure decreases whilst the inward pressure contracts the star until it is so hot and dense for nuclear fusion to occur
- Once the density increases, nuclear fusion starts up again which causes the star to expand
- this fusion form heavier elements (up to iron)
What is the lifecycle of stars the size of our Sun?
- Nebula (cloud of dust and gas)
- Protostar (attractive force of gravity pulls the dust and gas together)
- Main sequence star: stable period where inward pressure= outward pressure
- Red giant: the expansion after the star has contracted and undergoes nuclear fusion that forms elements up to iron
- White dwarf: once the red giant becomes unstable it expels its outer layer and leaves behind a hot, dense, solid core
- Black dwarf: over time the white dwarf gets cooler and darker as it emits its energy
What is the lifecycle of stars much bigger than our Sun?
- Nebula
- Protostar
- Main sequence star
- Red super giant: undergo even more nuclear fusion
- Supernova: the explosion of a red super giant which forms elements heavier than iron which are ejected across the universe
- Neutron star: if the star is very big it will condense into a very dense core called a neutron star
- Black hole: if the star was even bigger it might collapse in on itself and form a black hole
What are natural satellites?
e.g. our moon, are not man-made
What are artificial satellites?
man made, e.g. communication, orbiting telescopes
List the planets in the solar system from the closest to the sun
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
The centripetal force which allows planets and satellites to maintain their circular orbit is…
gravity
What is an orbit?
The curved path of one celestial object around another celestial object
Describe the movement of an object travelling in a circle
- constantly changing direction so constantly accelerating
- there is a strong gravitational force which directed towards the centre of the circle
- the object keeps accelerating towards what it’s orbiting but the instantaneous velocity keeps it travelling in a circle
How does the size of the orbit affect the speed?
if the orbit is closer to the earth, there would be a greater gravitational force so the orbiting object would need to move faster
Explain what is meant by the term ‘red shift’
As an object moves away from us , the wavelength of light that the object emits gets longer so the light gets redder
What is the big bang theory?
theory which states the universe began from a very small region that was hot and dense and the region ‘exploded’ and started expanding
What evidence supports the Big Bang Theory?
the observation of red-shift in distant galaxies which suggests the universe has expanded from a single point
What is dark matter?
An unknown substance that holds galaxies together but does not emit electromagnetic radiation
What is dark energy?
The thing that causes the universe to quickly expand
