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.