The Doppler Effect & Hubble
Objectives Explain the Doppler Effect. Describe Hubble s discoveries. Explain Hubble s Law.
The Doppler Effect The Doppler Effect is named after Austrian physicist Christian Doppler who proposed it in 1842.
The Doppler Effect The Doppler Effect is the change in frequency and wavelength of a wave that results when the source of the wave is moving relative to an observer. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and moves away from an observer.
The Doppler Effect The received frequency is higher (compared to the emitted frequency) as the vehicle approaches, is identical during the instant the vehicle passes by, and is lower as the vehicle moves away. http://www.colorado.edu/physics/2000/apple ts/doppler2.html
The Doppler Effect Explained When the source of the waves (siren or horn) is moving toward the observer, each successive wave is emitted from a position closer to the observer than the previous wave. Because it has less distance to travel, each wave takes slightly less time to reach the observer than the previous wave. So, the time between the arrival of each wave at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between wave fronts is reduced; so the waves "bunch together".
The Doppler Effect Explained Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave. So the arrival time between waves is increased, reducing the frequency. The distance between waves is increased, so the waves "spread out or stretch.
The Doppler Effect
Doppler Simulation http://astro.unl.edu/classaction/ani mations/light/dopplershift.html
Edwin Hubble 1950 s American astronomer Discovered the existence of galaxies other than the Milky Way. He used Doppler Shift to see that galaxies are moving.
Doppler Effect and EMR The Doppler Effect also applies to electromagnetic radiation. Just like sound waves, EMR waves increase or decrease in frequency if the object emitting them is moving towards or away from an observer.
Redshift and Blueshift If the object is moving away from observer, the wavelength (of the waves moving back toward the observer) stretches and frequency decreases resulting in REDSHIFT. If the object is moving towards an observer, the wavelength compresses and the frequency increases resulting in BLUESHIFT. Remember the spectrum.
DOPPLER EFFECT
Redshift in Space If an object in space were moving away from Earth, the EMR waves travelling back to Earth would stretch or increase in wavelength and decrease in frequency and shift toward the red end of the spectrum.
Blueshift If an object in space were moving toward Earth, the EMR waves moving toward Earth would compress or decrease in wavelength and increase in frequency and shift toward the blue end of the spectrum.
Hydrogen
Red Shifted Galaxies Hubble observed that the light spectra coming from most galaxies was red shifted (observation). This meant that the galaxies were moving away from Earth (inference).
Hubble s Law Hubble s Law: the degree of redshift observed in the light spectra from other galaxies increases in proportion to the galaxies distance from Earth. OR the greater the degree of redshift, the farther away a galaxy is, and the faster it is moving. This law would help establish that the known universe is expanding = the BIG BANG THEORY.
Redshift vs. Distance
Hubble s Law
Red Shifted Galaxies When we observe the light spectra coming from known galaxies, most are red shifted (observation). Most galaxies appears to be moving away from us therefore, the universe is expanding (inference).