Scientists are able to estimate the age of the Universe by looking for the oldest stars and by measuring the rate of expansion of the Universe.
The Doppler EffectWhen a car is standing still, the sound waves going out from its horn are evenly spaced. When the car is moving toward an observer, however, the waves bunch together ahead of the source. This causes the pitch of the horn to rise. Just as the car passes the observer, the pitch of its horn suddenly drops to a lower tone as the sound waves become more spread apart.
This same phenomenon can occur with light waves and its one source of evidence scientists use to estimate the age of the Universe.
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Redshift
- Astronomers determined the Universe is expanding based on the color of light emitted from galaxies and stars just like the doppler effect.
- Edwin Hubble examined a galaxy's spectrum (light waves) of many galaxies at various distances from Earth. By examining a galaxy's spectrum, Hubble could tell how fast the galaxy was moving and whether it was moving toward our galaxy or away from it. Hubble discovered that almost all galaxies are moving away from us and from each other. This discovery was more evidence for the Big Bang theory.
As the Universe expands and galaxies move apart, the wavelength of light emitted from those galaxies is stretched. This shifts the light toward the red end of the spectrum and is called “red-shift”. The more distance a galaxy the more rapidly it is moving away from Earth.
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Topic Tips
- As the Universe expands and galaxies move apart, the wavelength of light emitted from those galaxies is stretched. This shifts the light toward the red end of the spectrum and is called “red-shift”. The more distance or faint a galaxy the more rapidly it is moving away from Earth.