We live in the Milky Way. It contains billions of stars. There are billions of galaxies in the Universe.
Red-Shift - Light from distant galaxies ---> frequencies slightly lower ---> shifted toward the red end of the spectrum.
The further away a galaxy is = the greater the red-shift.
More distant galaxies are moving away from us faster than the nearer ones are.
This provides evidence that the whole universe is expanding.
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The Big Bang
Key Words: Expanding, Big Bang
Red-Shifts give us evidence that the Universe is expanding out in all directions.
All the matter and energy must have been compressed into a very small space. Then it exploded and started expanding and the expansion is still going on now.
The age of the Universe can be estimated from the current rate of expansion ---> We think it was 13.7 billion years ago.
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Looking Into Space
Key Words: Telescope, Atmosphere, Satellite
Scientists use Telescopes to collect visible light from coming stars, and so see them.
They can also use telescopes to collect radiation from other parts of the spectrum. E.g. X-rays or Radio Waves.
The atmosphere is a layer of gases surrounding the Earth.
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