1. Red Shift/Blue Shift The Doppler Effect with Light

2. 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.

3. Electromagnetic Spectrum
In which direction does the wavelength increase?
Increasing λ
In which direction does the frequency increase?
Increasing f

4. Stationary Wave SourcesL R
Q: Does either eye (left or right) observe a different wavelength light?
Q: Does either eye (left or right) observe a different wavelength light?
A: No. Both eyes observe the same wavelength, yellow, light.

5. Moving Wave Sources L R
Q: Does either eye (left or right) observe a different wavelength light?
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.

6. Red Shift / Blue Shift, Notes:
Wave source approaching (blue shift)
wave fronts are squished together
wavelength is shorter, frequency is higher
so it appears bluer
Wave source moving away (red shift)
wave fronts are spread apart
wavelength is longer, frequency is lower
so it appears redder
Q: What happens to the light the left eye sees?
Red Shift Blue Shift No Shift
Q: What happens to the light the right eye see?
Red Shift Blue Shift No Shift

7. What Color Does Ashley See?
What Color Does Jessica See?

8. 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.

9. 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 head. What colors will you see?
red  ?
?  blue

10. You Would See Green  Yellow Blue  Green Red Infrared*
* Note: Human Eyes Can’t See Infrared

11. 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).

12. What We See
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
This is the absorption spectrum (pattern of black lines) from a close star like our sun.
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.

13. What We See
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
If the nearby galaxy wasn’t moving, the absorption spectrum
(the pattern of black lines) would be in the same place.

14. Is the pattern red shifted or blue shifted?
What We See
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
Is the pattern red shifted or blue shifted?

15. What We See The pattern is red shifted
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
The pattern is red shifted
since it is shifted towards the red side of the spectrum.

16. What We See The pattern is red shifted. — So —
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
The pattern is red shifted.
— So —
Is the nearby galaxy moving towards us or away from us?

17. What We See The pattern is red shifted. — So —
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
The pattern is red shifted.
— So —
Is the nearby galaxy moving towards us or away from us?

18. The bigger the shift, the faster the light source is moving.
What We See
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
The bigger the shift, the faster the light source is moving.

19. What We See Which is moving away faster:
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
Which is moving away faster:
the nearby galaxy or the faraway galaxy?

20. What We See Which is moving away faster:
Close
Star
Nearby Galaxy
Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.
Which is moving away faster:
the nearby galaxy or the faraway galaxy?

21. What We See Close Star Nearby Galaxy Faraway Galaxy
Really Faraway Galaxy
The pattern of black lines come from hydrogen.
As we look at objects further from earth, is the pattern shifted?
Is it a red shift or a blue shift?  Red shift, so the faraway galaxies, are going away from us.

22. Your Turn The further away a galaxy is, the bigger the ______ shift.
So far away galaxies are moving away _______.
red
blue
slower
faster

23. Your Turn The further away a galaxy is, the bigger the ______ shift.
So far away galaxies are moving away _______.
red
red
blue
slower
faster

24. Your Turn The further away a galaxy is, the bigger the ______ shift.
So far away galaxies are moving away _______.
red
red
blue
faster
slower
faster

25. Scientists’ Conclusions
The further away a galaxy is, the bigger the red shift.
So far away galaxies are moving away faster.
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.
Scientists’ Conclusions