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30 Read and answer: a) Why does the tilt of the Earth's axis cause the seasons? What is the other cause? b) The grape harvest in Spain takes place in September. However, in South Africa it takes place in March. Why? 31 The distance between the Earth and the Sun changes slightly over the course of the year. a) How can this fact be proved? b) On 3rd January, the Earth is at the point in its orbit where it is closest to the Sun. On 3rd July, it is at its furthest. Explain why it is much colder in the Northern Hemisphere on 3rd January than on 3rd July. 32 Imagine a square house, with the façades oriented to the four cardinal points. a) On which façade does the Sun shine throughout the day in winter, from sunrise to sunset? b) On which façade does the Sun not shine all day? 33 The ecliptic plane is an imaginary plane that passes through the centre of the Earth and also through the centre of the Sun. a) Does it also pass through the centre of the Moon? b) Does this only happen occasionally? How often and when? 34 Put these images from the lunar cycle in order. Identify the new Moon, waxing Moon, full Moon and waning Moon. Start with the full Moon. 35 In pairs, make a model of the Earth, the Sun and the Moon. Use the model to simulate eclipses of the Sun and the Moon. a) D raw a sketch of the model before you make it. Think about what materials you need to make it. b) E ach person chooses a type of eclipse and uses the model to explain to their partner what happens during the eclipse. 36 There is a mistake in the drawing below. Explain what it is. Hint: pay attention to the clock and the Moon. 37 For there to be a solar eclipse, there must be a full Moon. So why is there not a solar eclipse every time there is a full Moon? 29 A S T R O N O M Y A N D M AT H E M AT I C S . The average distance between the Earth and the Sun is 150 million kilometres. The speed of light in a vacuum is 300 000 km/s. Bearing in mind the speed of light, how long does a ray of light take to reach Earth from the Sun? A D G B E H C F I 1 c h e c k yo u r p r o g r e s s 31

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