Astronomy & space · Grades 5–9
Solar-system structure and scale · revision notes
The Sun is a star at the centre of the planetary system. Planets, moons, small bodies, gas and dust form a gravitationally interacting system.
Key ideas and conditions
Architecture
The Sun is a star at the centre of the planetary system. Planets, moons, small bodies, gas and dust form a gravitationally interacting system.
Categories
A planet, a moon and a star are different kinds of object. A moon orbits a larger nonstellar body; stars sustain fusion during their main-sequence phase.
Distance units
An astronomical unit is a defined length close to the mean Earth-Sun distance. Light-years also measure distance, not time.
Scale models
One scale rarely shows both body sizes and orbital distances conveniently. State what is scaled and what has been exaggerated.
Explain without looking
- Which force primarily binds planetary orbits on solar-system scales?
- Explain why counting only planets does not describe all solar-system matter.
Further reading and review references
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