Topic 11 – Exploring the Solar System — Edexcel GCSE Astronomy
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Topic 11 – Exploring the Solar System explained
A comet has three named parts. The nucleus is the solid, icy body at the centre, often described as a dirty snowball of ice, dust and rocky material.
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As the comet approaches the Sun, solar heating turns some of the ice into gas, and this gas and dust form the coma, a glowing cloud around the nucleus. The tails also develop as the comet nears the Sun. The dust tail is curved and lags behind the comet's path, while the ion tail is straighter and points away from the Sun. Learn to label a diagram of a comet and to explain why the coma and tails grow brighter and longer near the Sun and fade when the comet is far away.
Your focus
- Label the nucleus, coma and tails on a diagram of a comet.
- Describe the shape and direction of the dust tail and the ion tail.
- Explain how the coma and tails change as a comet moves towards or away from the Sun.
Topic 11 – Exploring the Solar System exam tips
Marking Points
- Identifies the nucleus as the solid, icy central body of a comet.
- Describes the coma as the cloud of gas and dust surrounding the nucleus.
- States that the coma forms when solar heating turns some of the comet's ice into gas.
- Identifies the dust tail as curved and lagging behind the comet's motion.
- Identifies the ion tail as straighter and pointing away from the Sun.
- Explains that the coma and tails develop as the comet approaches the Sun and fade when it is far away.
Examiner Tips
- 💡Sketch a quick labelled diagram of the nucleus, coma and both tails before answering a structure question.
- 💡Use the phrase 'away from the Sun' whenever you describe the direction of the tails.
- 💡Link each part to the comet's distance from the Sun, because heating drives the coma and tails.
Common Mistakes
- Calling the coma the solid part of the comet: the error is mixing up the parts; the correction is that the nucleus is solid and the coma is the surrounding gas and dust cloud.
- Saying the tails point towards the Sun: the error is reversing the direction; the correction is that the tails point away from the Sun.
- Describing both tails as identical: the error is ignoring their shapes; the correction is that the dust tail is curved and lags behind, while the ion tail is straighter.
- Thinking the coma and tails are always present: the error is ignoring the comet's orbit; the correction is that they develop as the comet nears the Sun and fade when it is far away.