Red Shift/Blue Shift
The Doppler Effect with Light
Scientists Say:
The universe started like this:
Here we look at some java applets:
2D big bang
3D big bang
Today we’re going to learn why.
Electromagnetic Spectrum
In which direction does
Increasing
the wavelength
λ
increase?
In which direction Increasing
does the frequency
f
increase?
Stationary Wave Sources
L
Q: Does either eye (left or right) observe a different wavelength light?
A: No. Both eyes observe the same wavelength, yellow, light.
R
Moving Wave Sources
L
R
Q: Does either eye (left or right) observe a different wavelength light?
A: Yes. The left eye will see longer wavelength light and the right eye will see
shorter wavelength light.
Red Shift / Blue Shift, Notes:
L
R
b. Wave source approaching
(blue shift)
i. wave fronts are
squished together
ii. wavelength is shorter,
frequency is higher
iii. so it appears bluer
a.Wave source moving away
(red shift)
i. wave fronts are
spread apart
ii. wavelength is longer,
frequency is lower
iii. so it appears redder
Q: What happens to the light the left
righteye
eyesees?
see?
Red Shift
Blue Shift
No Shift
What Color Does Ashley See?
What Color Does Jessica See?
A Person Stands on a Planet
The Planet is Flying Away
The person is holding
a red and a blue light
bulb. A green light
bulb grows out of their
head.
Draw What You’ll See:
Label the colors of the light bulbs!
green ?
The person is holding a red
and a blue light bulb. A green
light bulb grows out of their
What colors will
you see?
head.
red  ?
?  blue
Green  Yellow
Red Infrared*
You
Would
See
* Note: Human Eyes Can’t See Infrared
Blue  Green
The Sun & The Stars
• The sun is a star.
• The sun and the stars are all made out of
hydrogen.
• Light from hydrogen leaves a distinctive
pattern of black lines (an absorption
spectrum).
What We See
Close
Star
Nearby
Galaxy
This is the absorption spectrum (pattern of black lines) from a
close star like our sun.
Faraway
Galaxy
Really
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
If the nearby galaxy wasn’t moving, the absorption spectrum
(the pattern of black lines) would be in the same place.
Really
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
Really
Faraway
Galaxy
Is the pattern red shifted or blue shifted?
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
The pattern is red shifted
since it is shifted towards the red side of the spectrum.
Really
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
The pattern is red shifted.
— So —
Really
Is the nearby galaxy moving towards us or away from us?
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
The pattern is red shifted.
— So —
Really
Is the nearby galaxy moving towards us or away from us?
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
Really
The bigger the shift, the faster the light source is moving.
Faraway
Galaxy
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
Really
Faraway
Galaxy
Which is moving away faster:
the nearby galaxy or the faraway galaxy?
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
Really
Faraway
Galaxy
Which is moving away faster:
the nearby galaxy or the faraway galaxy?
What We See
Close
Star
Nearby
Galaxy
Faraway
Galaxy
Really
Faraway
Galaxy
Your Turn
The further away a galaxy is,
the bigger the ______ shift.
red
blue
So far away galaxies are moving away _______.
slower
faster
Your Turn
The further away a galaxy is,
red shift.
the bigger the ______
red
blue
So far away galaxies are moving away _______.
slower
faster
Your Turn
The further away a galaxy is,
red shift.
the bigger the ______
red
blue
faster
So far away galaxies are moving away _______.
slower
faster
The further away a galaxy is, the bigger the red
shift.
So far away galaxies are moving away faster.
Scientists’ Conclusions
• The galaxies must have been close together in
the past.
• A tremendous explosion (a big bang) must have
made everything explode outward.
• That’s why the fastest galaxies are the furthest
away.