What makes up the Solar System, how do stars form and change, and what is the evidence for the Big Bang?
The Solar System and orbits, the life cycle of a star, and red shift as evidence for an expanding universe and the Big Bang theory.
A CCEA GCSE Double Award Science (Physics Unit P2) answer on the Solar System and orbits, the life cycle of a star from nebula to its final stages, and red shift as evidence for an expanding universe and the Big Bang theory.
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What this dot point is asking
CCEA Double Award wants you to describe the Solar System and orbits, the life cycle of a star, and red shift as evidence for an expanding universe and the Big Bang. The star life-cycle and the red-shift explanation are common extended-response questions.
The Solar System
Planets follow nearly circular orbits; comets have very stretched (elliptical) orbits, so they speed up when close to the Sun and slow down far away.
The life cycle of a star
During the main-sequence stage, the inward pull of gravity is balanced by the outward push from the energy released by nuclear fusion of hydrogen into helium.
Red shift and the Big Bang
This observation is evidence that the whole universe is expanding, which supports the Big Bang theory: that the universe began from a single tiny, hot, dense point and has been expanding ever since.
Where the chemical elements come from
Stars are also where the chemical elements are made. During a star's main-sequence life, hydrogen fuses into helium. In larger stars, later stages fuse helium into heavier elements up to iron. Elements heavier than iron are made in the extreme conditions of a supernova, which then scatters them across space. The atoms in your body, and in the rocks of the Earth, were made inside earlier generations of stars, which is the literal meaning of the saying that we are "made of stardust".
Examples in context
- Example 1. Why the Sun is stable
- The Sun is a main-sequence star: the inward gravity is balanced by the outward pressure from fusion, so it stays the same size for billions of years.
- Example 2. Evidence for the Big Bang
- As well as red shift, the faint cosmic microwave background radiation found across the whole sky is further evidence that the universe began hot and dense and has cooled as it expanded.
- Example 3. Comets
- A comet has a very stretched orbit, so it spends most of its time far from the Sun moving slowly, then speeds up and grows a bright tail as it swings close to the Sun, where the Sun's heat vaporises some of its ice.
Try this
Q1. What force keeps the planets in orbit around the Sun? [1 mark]
- Cue. Gravity (the gravitational force of the Sun).
Q2. State the final stage of a star the size of the Sun. [1 mark]
- Cue. A white dwarf.
Q3. What does red shift tell us about distant galaxies? [2 marks]
- Cue. They are moving away from us, and the more distant ones move away faster (the universe is expanding).
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA-style4 marksDescribe the life cycle of a star similar in size to the Sun, from its formation to its final stage.Show worked answer →
A star forms from a cloud of dust and gas (a nebula) pulled together by gravity, becoming a protostar that heats up until fusion begins.
It then becomes a stable main-sequence star (like the Sun now), where fusion of hydrogen balances gravity.
When the hydrogen runs low it swells into a red giant.
Finally it sheds its outer layers and the core collapses to a white dwarf, which cools over time.
Markers reward nebula, main sequence star, red giant, and white dwarf in the correct order for a Sun-sized star.
CCEA-style4 marksExplain what red shift is and how it provides evidence that the universe is expanding.Show worked answer →
Red shift is the shift of light from distant galaxies towards the red (longer wavelength) end of the spectrum.
This shows the galaxies are moving away from us.
More distant galaxies show a greater red shift, so they are moving away faster.
This means the whole universe is expanding, which supports the Big Bang theory.
Markers reward red shift as a shift to longer wavelength, galaxies moving away, greater red shift for more distant galaxies, and evidence for an expanding universe (Big Bang).
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Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)