The Doppler Shift
The Doppler Shift
The Visible SpectrumWhite light splits into the colors of the rainbow when passed through a prism.
The Visible Spectrum
Red Orange Yellow Green Blue Indigo Violet
The Visible Spectrum
R O Y G B I V
I would like to introduce...
RO Y G BIV
Sometimes it gets reversed...
RO Y G BIV
Sometimes it gets reversed...
RO Y G BIV
Sometimes it gets reversed...
VI B G YOR
But the order makes no difference.
(Roy’s evil twin brother.)
There’s more to the spectrum than what you can
see.
Rad
io W
aves
Mi c
r ow
ave s
Infr
ared
(IR
)
Ult
ravi
olet
(UV
)X
-Ray
s
Gam
ma
Ray
s
There’s more to the spectrum than what you can
see.
Pure White Light
Glowing Gas
Neon Light
The “fingerprint” of an element.
Glowing Gas
Hydrogen Light
When sound is made by a stationary object, you hear a
certain frequency...
Insert constant sound here
If you could see it, it would look like this...
But when the sound moves towards you, it sounds higher in
pitch.
Waves get compressed.
The faster the object moves, the higher the pitch.
Waves get compressed more.
When the object moves at the speed of sound, the waves
overlap...
...and you get a sonic boom.
Fly faster than sound, and you’re gone before the boom is
heard.
Fly faster than sound, and you’re gone before the boom is
heard.
Fly faster than sound, and you’re gone before the boom is
heard.
An on-line visualization:
• http://www.phy.ntnu.edu.tw/java/Doppler/Doppler.html
When the sound moves away, it sounds lower.
Waves are stretched.
What it Sounds Like.
Car 1
Bike 1
Prop 1
Whine Jet 1
Deep Jet
Prop2
Race1
Race2
Mortor
Prop2
Race1
Race2
The same shifting happens with the light from a moving star.
Lower Frequency Higher Frequency
The spectrum of hydrogen that is from a stationary source.
When the star is moving closer...
Stationary Hydrogen
“Blue Shifted” Hydrogen from star moving towards Earth.
And when a star moves away from us...
Stationary Hydrogen
Lines are shifted to the red end.
And when a star moves away from us...
Stationary Hydrogen
Lines are shifted farther to the red end.
Faster
Since the universe is expanding...
• All distant objects have a red shift.• The farther the object, the more
extreme the red shift.
Astronomers use this relationship between distance and speed to measure the distance to distant stars and galaxies.
