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Lesson 2: Classification keys

Extension worksheet:

Why classify?

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People classify or group all sorts of objects in an attempt to create a sense of order. There are many different ways to classify things. When you grouped the objects in your pencil case you may have done so according to what they are made of (wood – pencil or metal – scissors) or how they are used (writing – pencil and pen, or erasing – eraser and correction fluid). Classifying (or grouping) helps people see similarities and differences within and between groups.

Scientists in all fields classify objects to suit a particular purpose. For example, chemists may classify substances as elements, compounds or mixtures; biologists may classify things as living or non-living and geologists may classify rocks as igneous, sedimentary or metamorphic. When classifying things, scientists usually follow an agreed set of rules that form a classification system.

Part A

When you look in the sky at night you can usually see many different objects. Astronomers would classify some of the objects as stars, others as planets and so on. To do this they need to know the differences between objects.

1. Your task is to design and present a classification system that could be used to classify objects seen in the night sky. You will need to identify features of the objects, which will enable you to classify them into distinct groups eg, planet, star.

You may find these websites helpful:

‘What is the physical difference between a star and a planet?’, Curious about Astronomy?, Cornell University website http://curious.astro.cornell.edu/question.php?number=548 (20 January 2004)

‘Why do stars twinkle?’, Curious about Astronomy?, Cornell University website http://curious.astro.cornell.edu/question.php?number=114 (6 November 2002)

Part B

When astronomers use powerful telescopes, such as the Hubble telescope, they can see billions of objects in the night sky. Some of these objects have been classified as galaxies – groups of millions of stars.

To understand more about galaxies, astronomers classify them according to their shape. They have estimated there are roughly one hundred billion galaxies throughout our universe. As there are so many galaxies and not many astronomers, a project called ‘Galaxy Zoo’ has been developed where volunteers can help classify all the galaxies that have been identified so far.

2. One of the criteria for a successful classification system is that it creates order, with items of similar features being placed together

a) Your task is to evaluate the Galaxy Zoo classification system. Justify whether or not you think it is a successful classification system.

Log onto the Galaxy Zoo website http://www.galaxyzoo.org/ (accessed 12 August 2013) and click on ‘Begin Classifying’.