Task 4: Explaining the evidence [M6]

First try these demonstrations

A: Galaxies

1.     Take a round balloon and draw on it six small galaxies, each about 5mm across Make your galaxies roughly evenly spaced around the balloon.

2.    Choose any one of the galaxies, and mark it ‘A’ so that you remember which it is.  Make a mental note of the distances from this galaxy to its nearest neighbours.

3.    The balloon represents space itself.

4.     Blow up the balloon to represent the expansion of space

5.    Again check the distances from galaxy A you selected to its nearest neighbours


Answer these questions

a)    Sketch the balloon with its galaxies before and after you blew it up.














b)   If people living somewhere in galaxy A observe the motions of their neighbour galaxies, what will they notice?  Why might they think their own galaxy is the centre of the universe?

c)    Would people in a different galaxy observe the same overall effect, or something different?


d)   As time goes by, the real universe behaves rather like this balloon.  What do you think our astronomers must have observed about the motion of our neighbouring galaxies?


B: Light

When space itself expands, any light waves travelling across it become stretched.

1.     Take a long balloon, and use a pen to draw a wave along it

2.     Blow up the balloon to represent the expansion of space.  Observe what happens to the wave.




Answer the following questions

a)  Sketch the balloon before and after.













b)  How did the wavelength change when you blew up the balloon?





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