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EXPANDING UNIVERSE QUESTIONS

Pupil Worksheet -- The Expanding Universe

READ THE FOLLOWING PASSAGE CAREFULLY

Expanding Universe

Astronomers believe that the Universe is expanding. It was found that, the more distant or fainter a galaxy, the more rapidly it was moving away from us, e.g. NGC 669 is moving away from us at 5 million metres per second and is believed to be 250 million light years away. The cluster of galaxies Abel 2065 is moving away from us at 22 million metres per second and is believed to be about 1,100 million light years away. This observation was put in a law called after Erwin Hubble in which the distance is related to the speed that the galaxy or cluster of galaxies is moving away from us

Distance = redshift x Hubble constant.

There is a degree of dispute about the value of the Hubble constant. For the purposes of this project we will use the figure of 20,000 metres per second per million light years

Evidence

The evidence that stars and galaxies are moving AWAY comes mainly from the RED SHIFT of the light spectrum received from them. Most people have heard the DOPPLER effect as the sound of, say a police siren, changes from high pitch when approaching to a low pitch when receding from the observer. The change in pitch could be used to measure the SPEED of the car (in fact, RADAR guns used in speed traps do use this method).Similarly, the change in light FREQUENCY, which of course changes the COLOUR of the light, tells astronomers the SPEED of the star either towards us or away from us.

Theory

One theory about the Universe is that it all started with the BIG BANG; before that, there was NO space and NO time. It is quite easy to calculate the age of the Universe by finding the time when all the stars and galaxies must have been in one PLACE. Current measurements give the age within the range 10 to 20 thousand million years.

ANSWER THE FOLLOWING QUESTIONS

1 - a. Calculate the time (in years) that the Abel 2065 cluster of galaxies and our Sun have been moving apart. Use the formula


          VELOCITY   =   DISTANCE    TIME


          where 1 light year  =  (3 x 108 )    x  (3.7 x 107 )metres
                                 velocity of    x  seconds in
                                 light             a year

b. What assumptions have been made about the distances and the velocity?

2 - The diagrams show the sound waves produced by a siren on a car

a. State why the two people hear the same note when the car is stationary.
b. Now the car moves from A to B. Copy the diagram and complete the sound waves.

c. Use the formula WAVE VELOCITY = FREQUENCY X WAVELENGTH to
explain why A hears a low pitched sound and B hears a high pitched sound.

3 - Explain why a light spectrum shifted to the RED end of the spectrum tells us that the light source is moving away from us.

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