146 Chapter 3 The Universe Was Born With a Big Bang
Back to the play:
“Hubble’s Great
Discovery—Act II”
What are you
investigating
now?
We, I’ve bn lking
at observational data
for the spectra of
other galaxies that I
received from Vesto
Slipher of the Lowe
Observatory, and...
...it's aarent that
the wavelength
of the light is
shifted in the red
direction.
bule pipe
What did
you say?!
Kaa?
Soy...
what does
"shifted in the
red direction"
mean?
Disaointed
Now...
Redshift is...
er...um...
Hule’s Great Discovery 147
we-oh!
we-oh!
The Profeor
has gone nuts!
Think of an
ambulance...
As it aroaches,
the pitch of the
siren gets higher...
...and then once it paes
and moves farther away, the
pitchgets lower, right?
...that’s the
Doler
eect!
Since sound is a wave, when the
sound source comes closer,
the wavelength gets shorter,
causing the sound to become
higher in pitch. When the sound
source moves farther way, the
wavelength gets longer, and
the sound drops in pitch.
148 Chapter 3 The Universe Was Born With a Big Bang
Since light also
travels in waves,
the same kind of
phenomenon ours.
When a light source
aroaches, the light coming
from it shifts toward blue,
and when the light source
recedes, the light coming
from it shifts toward red.
But how is that
related to
galaxies?
Wait until
you s the
next act.
Did you say that
the spectra of
other galaxies are
shifted in the red
direction?
Yes...
Isn’t that
just a simple
observation
eor?
If the shift
dierence were
the same for a
galaxies, I would
have agrd, but...
...there are subtle
dierences in the
shift, depending on
th e ga laxy.
Light spectrum
Red
Yeow
Grn
Blue
Redshift ours for a
receding object.
Amazing!
...Yes?
We, it means
that the galaxies
are moving away
from us at a high
spd!
So the fact that
the spectra are
redshifted...
I also examined
the spectra of
the galaxies and
tried to calculate
a coelation
betwn the
distance and the
redshift.
When I did this, I found
that the farther away a
galaxy was, the greater
the spectral oset due
to redshift was.
150 Chapter 3 The Universe Was Born With a Big Bang
Therefore...
...therefore?
The universe is
expanding even as
wespeak!
Indd!
The Universe is sti
expanding?!
Yes, I' explain
that now.
Huh?!

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