Download 26.5 Guided Notes

Name________________________________________ Period ______________
26.5: The Expanding Universe Guided Notes
Expanding Universe
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Telescopes are like time machines because they show what happened in the distant past.
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The Electromagnetic Spectra and Visible Light
Blue = Shorter Wavelengths & Red = Longer Wavelengths
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The Doppler Effect (like when an ambulance goes by) helps to determine how fast stars or
galaxies are moving toward or away from Earth.
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When a star or galaxy is moving toward earth, the lines in its spectrum are shifted toward the
shorter, blue wavelengths.
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The American astronomer Edwin Hubble observed a red shift in the light spectra of galaxies
which shows that the universe is expanding. A blue shift would indicate that the universe was
condensing.
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Hubble’s Law says that the speed at which a galaxy is moving away from Earth is proportional to
its distance from us.
The Big Bang Theory
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Astronomers theorize that the universe came to be at a single moment, in an event called the
Big Bang. All matter and energy of the universe is thought to have been concentrated in an
incredibly hot region smaller than the period at the end of this sentence then exploded in an
instant 13.7 billion years ago.
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2 Main Pieces of Evidence for the Big Bang Theory
1. Existence of cosmic microwave background radiation
2. Red shift in the spectra of distant galaxies
Continued Expansion
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Rate of expansion seems to be increasing…if so, the universe will expand forever
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If the mass of the entire universe is large enough, it is possible that the expansion will stop and
the universe will begin to condense…the big bang could reverse!
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Scientists are unsure because they are not sure as to how much dark matter really exists.
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Dark matter is just matter that does not give off radiation so it can only be detected by
observing the gravitational effects it has on visible matter like stars.