The Earth and Beyond

The Universe - Big Bang - Red-Shift - Expanding Universe.

A red-shift means that other galaxies are moving away from us.

When light or sound is emitted (given out) from an object
it will have a particular wavelength.
The wavelength will change
if the object is moving towards you or away from you.

Imagine that an object which is moving towards you
is emitting 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 now only takes up 1 - 0·1 metres, or 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.
(continued on the next page).

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