The Solar System
Within our solar system there is one star, the Sun, plus the eight planets and the dwarf planets that orbit around the Sun. Natural satellites, the moons that orbit planets, are also part of the solar system.
Our solar system is a small part of the Milky Way galaxy.
The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction.
At the start of a star’s life cycle, the dust and gas drawn together by gravity causes fusion reactions
In a main sequence star, fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star due to fusion energy.
Question: Describe how a star is formed. (2 marks)
- a nebula of dust and gas
- is pulled together by gravity
Question: The Sun is in the group of main sequence stars. These stars are stable.
Explain why a star remains stable. (2 marks)
- expansion due to fusion energy
- in equilibrium with gravitational collapse
A star goes through a life cycle. The life cycle is determined by the size of the star.
The life cycle of a star dependent on its size:
- the size of the Sun: nebula – protostar – main sequence star – red giant – white dwarf – black dwarf
- much more massive than the Sun: nebula – protostar – main sequence star – red supergiant – supernova – neutron star – (possibly) black hole
Fusion processes in stars produce all of the naturally occurring elements. Elements heavier than iron are produced in a supernova.
The explosion of a massive star (supernova) distributes the elements throughout the universe.
Fusion processes lead to the formation of new elements. When the star becomes a red super/giant there is no hydrogen left for fusion so it fuses larger elements to create elements up to the size of iron.
Question: The Earth contains elements heavier than iron.
Why is the presence of elements heavier than iron in the Earth evidence that the Solar System was formed from material produced after a massive star exploded? (1 mark)
elements heavier than iron are formed only when a massive star explodes
Question: Some stars are much more massive than the Sun.
Describe the life cycle of stars much more massive than the Sun, including the formation of new elements. (6 marks)
- fusion (processes in stars) produce new elements
- cloud of gas / hydrogen and dust OR nebula
- pulled together by gravity
- causing increasing temperature (to start the fusion process)
- (to become a) protostar
- hydrogen nuclei fuse to form helium nuclei
- and the star becomes main sequence
- hydrogen begins to run out
- helium nuclei fuse to make heavier elements
- up to iron
- the star expands (to become a)
- red super giant
- (the star collapses rapidly) and explodes
- called a supernova
- creating elements heavier than iron
- and distributing them throughout the universe leaving behind a neutron star
- or a black hole.
Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.
Planets orbit stars. Moons orbit Planets.
The artificial satellites that orbit earth usually occupy one of two types of orbit:
- Geostationary Orbit: The satellite has an orbital period the same as the Earth so it is always in the same position above the Earth. GPS and Communication satellites are in geostationary orbit.
- Low Polar Orbit: The satellite will orbit the planet as the planet rotates so it can see the entire planet over time. Spy satellites and mapping satellites use this type of orbit.
For circular orbits, the force of gravity can lead to changing velocity but unchanged speed; this is because velocity is a vector and has direction.
For a stable orbit, the radius must change if the speed changes. If a satellite slows down it will move to an orbit further from Earth to remain stable.
Question: Explain why the velocity of the satellite changes as it orbits the Earth. (3 marks)
- gravity causes the satellite to accelerate (towards the Earth)
- the acceleration causes a change in direction
- velocity changes because direction changes
Origins of The 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.
The Big Bang theory suggests that the universe began from a very small region that was extremely hot and dense.
Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding (moving away) ever faster.
There is still much about the universe that is not understood, for example dark mass and dark energy.
Question: The Big Bang theory is one model used to explain the origin of the universe.
How does the Big Bang theory describe the universe when it began?
hot and dense
Question: Describe the relationship between the speed of a galaxy and the distance the galaxy is from the Earth.
The further away a galaxy is from Earth, the fastest the galaxy is moving away from Earth.
Question: Scientists have observed that the wavelengths of the light from galaxies moving away from the Earth are longer than expected.
What name is given to this observation?
Question: The size of the red-shift is not the same for all galaxies.
What information can scientists find out about a galaxy when they measure the size of the red-shift the galaxy produces?
The distance for earth
The speed the galaxy is moving away from earth