Describe the similarities and distinctions between the planets, their moons, and artificial satellites.
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GCSE Physics Revision
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GCSE Physics revision
Orbital motion, natural and artificial satellites
Solar system; stability of orbital motions; satellites (physics only)
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Apply the scientific explanation of orbital motion, natural and artificial satellites to a relevant example.
Analyse a new situation involving orbital motion, natural and artificial satellites and explain the scientific reasoning.
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Key knowledge
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Satellites: Natural and Artificial
- Any object that orbits a planet is called a satellite, and these can be either natural or artificial.
- Natural satellites, such as the Moon, are not man-made, whereas artificial satellites are man-made and include communication satellites and orbiting telescopes.
Structure of Our Solar System
- The solar system consists of our central star, the Sun, orbited by eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
- The term 'solar system' is specific to our Sun and its planets, while any other star with orbiting planets is referred to as a star system.
- All eight planets travel in slightly elliptical orbits, meaning their paths are slightly squashed circles rather than perfect circles.
Asteroids and Comets
- Asteroids are made mostly of rock and metal and are mainly found in the asteroid belt located between Mars and Jupiter.
- Comets are made of ice and dust and orbit the Sun in significantly more elliptical orbits, often travelling to the very outskirts of the solar system.
Galaxies and the Milky Way
- A galaxy is a massive collection of billions of stars, most of which have their own star systems, all held together by gravity.
- Our solar system belongs to the Milky Way galaxy and is located about halfway along one of its spiral arms.
- Notable stars in the Milky Way include Polaris (the North Star), Betelgeuse (a bright reddish star), and Proxima Centauri (the closest star to us after the Sun).
The Universe
- The universe is a vast expanse scattered with billions of galaxies, separated by unimaginably large distances of mostly empty space.
- The scale of structures in the universe can be summarised as: the universe contains galaxies, galaxies contain billions of star systems, and star systems contain a central star orbited by planets.
Why We Need Special Units for Space Distances
- Distances in space are so enormous that using kilometres would produce unimaginably large numbers that are very difficult to work with.
- For example, Proxima Centauri is approximately 40 trillion km away from the Sun, which is a 4 followed by 13 zeros.
The Light-Year
- A light-year is the distance that light travels in one year, and is the standard unit used to measure distances in space.
- The speed of light is approximately 300,000 km/s, meaning light travels nearly 9.5 trillion km in a single year.
- Using light-years, Proxima Centauri is approximately 4.24 light-years away, and Polaris is approximately 433 light-years away from the Sun.
- Because light takes time to travel, the light we see from distant stars actually left those stars a very long time ago ā for example, the light from Polaris that we see today left the star over 400 years ago.