Physics for IGCSE & O level - The Earth In Space (Section 2 - No. 42)
What do scientists describe that makes the Universe is expanding?
Stars
Galaxies
The light year
The Doppler effect
Explanation
Neighboring galaxies in the Universe are typically a few million light years apart. The most distant galaxies observed from Earth are more than 13 billion light years away - their light has taken over 13 billion (13 x 10^9) years to reach us.
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