# Astronomy - Six-mark questions

Six-mark questions are often the questions that people find the most difficult. In all longer answer questions, but especially the six-mark ones, it is important that you plan your answer and not just rush into it. After all, you would plan an essay or short story before starting. Without a plan it is easy to stray away from the key point and lose marks, get steps in a process in the wrong order or forget key bits of information.

Six-mark questions will start with command words such as 'describe' or 'explain'. The command words 'describe' and 'explain' can be confusing. If you are asked to describe a graph, you will be expected to write about its overall shape, whether it is linear or curved, the slope of gradients etc. If you are asked to explain why a pattern or trend is seen in a graph, you will be expected to use your science knowledge, not just say what you see (which is a description), eg 'The graph shows the number of radioactive nuclei decreases as time increases. It does this because…'.

Explain how and why questions often have the word 'because' in their answer. Describe questions don't.

The number of marks per question part is given in this form '[6 marks]'. It is essential that you give as many different points in your answer as possible, linking these together. Often, you will be asked to compare two things: make sure that you include both in your answer otherwise, you are likely to limit your score to two marks out of six marks.

Edexcel questions courtesy of Pearson Education Ltd.

## Sample question 1 - Foundation and Higher

Question

A long time ago, astronomers thought that the Earth was the centre of the Universe. This was called the geocentric model. The evidence for this model came from observations of the sky using the naked eye. After the telescope was invented, astronomers quickly gathered evidence that showed that the geocentric model is not correct.

Describe the evidence both for the geocentric model and against the geocentric model. [6 marks]

Evidence for the geocentric model is that the Sun and stars move across the sky in the same direction everyday. They appear to be going around the Earth. However, Galileo observed moons which orbited Jupiter. This suggests that not everything orbits the Earth and that the geocentric model is not correct.

Plan the key points which you should include in your answer. Make sure you give a clear statement of any evidence that supports the geocentric model. Then give a clear statement of any evidence that is against the geocentric model. If you only give evidence one way then you will be limited to two or four marks. Give a number of pieces of evidence each way if you can.

## Sample question 2 - Higher

Question

Edwin Hubble discovered that the Universe was expanding. He did this by using observations of red-shift.

Explain what red-shift is and how it provides evidence that the Universe is expanding. [6 marks]

When a source of waves moves away from us, the waves are stretched, so the wavelength increases and the frequency decreases. The absorption lines move to the 'longer wavelength end' or 'red end' of the spectrum.

Light from nearly all galaxies shows red-shift. This means the galaxies are moving away from us. A greater red-shift indicates the galaxy is moving away faster. Further away galaxies have a greater red-shift. This suggests the Universe is expanding.

Plan the key points which you should include in your answer. Make sure you explain clearly that red-shift is referring to the change in wavelength and then discuss how it suggests the Universe is expanding. You will need to answer both parts of the question to score 6 marks.