Transcript Hubble`s Law Notes

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.
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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