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Edwin Hubble and Hubble’s Law The Doppler Effect • “The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is moving away.” http://www.physicsclassroom.com/class/waves/u10l3d.cfm Doppler Effect Well what does this have to do with the Big Bang? • Edwin Hubble was able to use the Doppler Effect with light to determine if stars/galaxies were moving away from us or toward us. • He was also able to use this data to determine exactly how fast the star/galaxy was moving. • Light travels in waves, exactly like sound does, so the Doppler Effect also works with light waves. • Edwin Hubble was able to use the Doppler Effect with light given off by distant stars/galaxies to determine if they were moving away from us or toward us. R O Y G B I V Redshift vs. Blueshift: Huh? • Redshift Definition: When an object is traveling away from the Earth, the light from this object is stretched out, making it look redder. • Blueshift Definition: When an object is traveling toward the Earth, the light from this object is compressed (squished), making it look bluer. Edwin Hubble • American astronomer known for confirming that other galaxies existed. • In 1929, discovered that the degree of “Redshift” observed in light spectra increased directly proportional with a galaxy’s distance from Earth. • Wait, what?... Hubble’s Law in Plain English • To put it simply, Hubble’s Law states: • The further away a galaxy or star is from the Earth, the faster it is moving. Further star = moving faster Earth! Closer star = moving slower Hubble & The Big Bang • Ok so we know that Hubble discovered most galaxies are redshifted but what does this have to do with the big bang? • Well, if Hubble discovered that most galaxies are moving away from us, that means the Universe is expanding. If the Universe is expanding, it must have started a single point, like a balloon. http://videos.howstuffworks.com/tlc/29804-understanding-hubbles-law-of-the-expanding-universe-video.htm Today’s value for Hubble’s Constant is around 75 km/s/Mpc