Red Shift/Blue ShiftThe 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

Increasing f

Increasing λIn which direction does the wavelength increase?

In which direction does the frequency increase?

Stationary Wave Sources

LR

Q: Does either eye (left or right) observe a different wavelength light?

A: No. Both eyes observe the same wavelength, yellow, light.

Q: Does either eye (left or right) observe a different wavelength light?

Moving Wave Sources

LR

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.

Q: Does either eye (left or right) observe a different wavelength light?

Red Shift / Blue Shift, Notes:

L R

a.Wave source moving away (red shift)

i. wave fronts are spread apartii. wavelength is longer, frequency is loweriii. so it appears redder

b. Wave source approaching (blue shift)i. wave fronts are

squished togetherii. wavelength is shorter,

frequency is higheriii. so it appears bluer

Q: What happens to the light the right eye see?

Red Shift Blue Shift No Shift

Q: What happens to the light the left eye sees?

Red Shift Blue Shift No Shift

What Color Does Ashley See?

What Color Does Jessica See?

A Person Stands on a PlanetThe 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!

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 ?

green ?

? blue

Red Infrared*

Green Yellow

Blue Green

You

Would

See

* Note: Human Eyes Can’t See Infrared

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

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

This is the absorption spectrum (pattern of black lines) from a close star like our sun.

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

If the nearby galaxy wasn’t moving, the absorption spectrum

(the pattern of black lines) would be in the same place.

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

Is the pattern red shifted or blue shifted?

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

The pattern is red shifted

since it is shifted towards the red side of the spectrum.

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

The pattern is red shifted.

— So —

Is the nearby galaxy moving towards us or away from us?

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

The pattern is red shifted.

— So —

Is the nearby galaxy moving towards us or away from us?

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

The bigger the shift, the faster the light source is moving.

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

Which is moving away faster:

the nearby galaxy or the faraway galaxy?

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

Which is moving away faster:

the nearby galaxy or the faraway galaxy?

What We See

CloseStar

Nearby Galaxy

Faraway Galaxy

Really Faraway Galaxy

fasterslower

The further away a galaxy is,

the bigger the ______ shift.

So far away galaxies are moving away _______.

Your Turn

red blue

red blue

The further away a galaxy is,

the bigger the ______ shift.

So far away galaxies are moving away _______.

Your Turn

slower faster

red

slower

red blue

The further away a galaxy is,

the bigger the ______ shift.

So far away galaxies are moving away _______.

Your Turn

faster

red

faster

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