GCSE Physics · AQA 8463 · Topic 4.8.1
Solar system, stability of orbital motions and satellites
Key points
- Our Solar System has one star (the Sun), eight planets, dwarf planets such as Pluto, and natural satellites (moons). It is part of the Milky Way galaxy.
- A star forms when a nebula of dust and gas is pulled together by gravity. When it is hot and dense enough, fusion of hydrogen starts.
- On the main sequence, the outward force from fusion energy balances the inward pull of gravity.
- Small stars: red giant → white dwarf → black dwarf. Large stars: red supergiant → supernova → neutron star or black hole.
- Fusion in stars makes elements up to iron; heavier elements form in supernovae, which spread them through the universe.
- Gravity provides the force for circular orbits. The speed is constant but the direction changes, so the velocity changes. (Higher tier) A smaller orbit needs a higher speed.
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Our Sun is one ordinary star among billions. This sub-topic covers what the solar system contains, how a star like the Sun forms and what will happen to it, and why planets, moons and satellites stay in their orbits instead of flying off or…
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