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What is a solar system
A collection of stars, planets, dwarf plants, asteroids, comets and satellites in orbit
What is a satellite
An object which orbits a planet- can be natural or artificial
What is an asteroid
Rock orbiting the sun
What is a comet
Icy rock orbiting the sun
What is a galaxy
A collection of stars and planets
Describe the formation of a main sequence star
Cloud of gas (mostly hydrogen) and dust called a nebula is disturbed, causing the particles to be pulled together by gravitational forces
As the particles get closer together, they form a hot rotating ball called a protostar
As the protostar becomes more dense, particles collide more and get hotter, as GPE is converted into thermal energy
If the protostar becomes hot enough, fusion may occur between hydrogen nuclei to form helium nuclei- this is a main sequence star. In a main sequence star, the inward gravitational forces are in equilibrium to the outward radiation pressure forces causes by nuclear fusion
Describe the second part of the life cycle of stars with a similar or lower mass than our sun
As the hydrogen runs out, the core collapses, and the outer layers expand to form a red giant
Since the core is now much denser and therefore hotter, helium nuclei now fuse to form heavier elements- nuclear fusion of elements as heavy as iron are formed here
When there are no more light elements left in the core, the core collapses in on itself as there is no outward pressure from fusion- the collapsed core forms a white dwarf, a hot iron sphere - it continues to glow from left over energy from fusion
Finally, as it runs out of energy, it cools down to form a black dwarf
Describe the second part of the life cycle of stars with a much greater mass than our sun
As the hydrogen runs out, the core collapses, and the outer layers expand more dramatically to form a red super giant, similar to a red giant
The red super giant then rapidly collapses, and forms a huge explosion called a supernova- in this all elements heavier than iron are formed
If the mass is great enough, the collapsed core will form a black hole, which has a gravitational field so strong nothing can escape it, not even light; if not it will form a neutron star, an incredibly dense star in which protons absorb electrons to form neutrons
How do circular orbits work
The forces of gravity pull the planet toward the centre of the sun and cause it to accelerate towards it
The force of the planet moving is perpendicular to the forces of gravity from the sun
As a result a circular orbit is produced
The magnitude of the velocity of the planet in circular orbit doesn't change, as it maintains the same speed (if the radius of the orbit is constant, so is the speed) but the direction of the velocity constantly changes, as the orbital path is circular
Explain why the velocity of a satellite changes as it orbits the Earth.
Force of gravity causes the satellite to accelerate towards the Earth
The acceleration causes a change in direction
Velocity changes because direction changes
For a stable orbit, what will happen to the radius of the orbit (the distance from the sun) if the planet speeds up
The radius must decrease as more gravitational forces are required to keep the planet in orbit, so it must move closer to the sun
Order these objects from lowest to highest orbit- geostationary satellite, GPS satellite which goes around the earth once every 12 hours, weather satellite which goes around the earth once every 3 hours
weather, GPS, geostationary (this completes one all orbit once every 24 hours, so moves at the same speed the earth spins, so keeps the same position above the earth)
The lower the satellite, the faster the orbit
How can red shift provide evidence of an expanding universe
There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red-shift.
The observed red-shift provides evidence that space itself (the universe) is expanding and supports the Big Bang theory.
What does the big band theory suggest
The Big Bang theory suggests that the universe began from a very small region that was extremely hot and dense.
What is seen the further a universe is from earth
The further away the galaxy, the more it is red shifted
This means the further away a galaxy, the faster it is moving away from us
This means that the galaxies is accelerating, from one small area away from each other
This shows the universe is expanding and supports the Big Bang theory
What is still unknown about the universe
Dark matter- there is unaccounted for mass in the universe which doesn’t interact with light- it means that the averse density of the universe is much larger than expected
Dark energy- scientists have proven, based on the observations of supernovae, that the universe is expanding exponentially, yet the only force which could cause this is gravity, which would do the opposite. So there must be some unknown force, driving the acceleration, and this is believed to be dark energy
