What are comets, asteroids, and meteors? -- Where do comets come from -- Why do comets have tails? -- What is a comet made of? -- Which are the most famous comets? -- Do comets ever crash? -- What are asteroids and where do they come from? -- Why do we need to study asteroids? -- What is the difference between meteors and meteorites? -- What are meteor showers? -- Fact file -- Glossary.