What you’ll learn10 learning objectivesChoose one objective for a focused lesson, or study the complete topic.6.1.2.1Contents: (a) the Sun (one star) (b)• Describe Solar System contents: (a) the Sun (one star) (b) eight named planets in order from the Sun (c) minor planets, including Pluto/dwarf planets and asteroid-belt asteroids (d) moons orbiting planets (e) smaller bodies, including comets and natural satellitesSyllabus objective6.1.2.2Four inner planets are small/rocky and• Know the four inner planets are small/rocky and the four outer planets are large/gaseous; explain this with the accretion model: gravity, many elements in gas/dust clouds, rotating cloud material and accretion-disc formationSyllabus objective6.1.2.3Strength of the gravitational field• Know: the strength of the gravitational field (a) at the surface of a planet depends on the mass of the planet (b) around a planet decreases as the distance from the planet increasesSyllabus objective6.1.2.4Time it takes light to travel a• Calculate the time it takes light to travel a significant distance such as between objects in the Solar SystemSyllabus objective6.1.2.5Sun contains most of the mass of the• Know: the Sun contains most of the mass of the Solar System and this explains why the planets orbit the SunSyllabus objective6.1.2.6Force that keeps an object in orbit• Know: the force that keeps an object in orbit around the Sun is the gravitational attraction of the SunSyllabus objective6.1.2.7Planets, minor planets and comets have• Know: planets, minor planets and comets have elliptical orbits, and recall that the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circularSyllabus objective6.1.2.8Analyse and interpret planetary data• Analyse and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet’s surfaceSyllabus objective6.1.2.9Strength of the Sun’s gravitational• Know: the strength of the Sun’s gravitational field decreases and that the orbital speeds of the planets decrease as the distance from the Sun increasesSyllabus objective6.1.2.10An object in an elliptical orbit• Know: an object in an elliptical orbit travels faster when closer to the Sun and explain this using the conservation of energySyllabus objective