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Stars and the Universe

The Universe - Big Bang - Red-Shift - Doppler Effect.

What is the Doppler Effect?

When light or sound is emitted (given out) from an object
it will have a particular wavelength and frequency.
The wavelength will change if the object is moving towards
you or away from you. This is called the Doppler effect.
The wavelength will increase and the frequency decrease
if the source of the wave is moving away from you.
If the source of the wave is moving towards you then the
wavelength will decrease and the frequency increase.

What causes the Doppler Effect?

Imagine that an object which is moving towards you
is emitting a wave with a wavelength of 1·0 metres.
During the time it has taken to emit one complete wave,
the object might have moved 0·1 metres towards you.
The wavelength has been shortened because the
whole wave is now only 1·0 - 0·1 metres = 0·9 metres.

The faster the object is moving towards you, the more
the wavelength is decreased and the frequency increased.
A decrease in the wavelength of light is called a blue shift.
See the next page.

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