IP1.31.3 Light and the doppler effect
Light and the doppler effect
© Oxford University Press 2011
IP1.31.3 Light and the doppler effect
Red shift
 Light from distant galaxies that are
moving has changes in its wavelength
due to the Doppler Effect.
 As galaxies move away from us the light
is stretched and its wavelength increases.
 Red light has the longest wavelength of
any colour, so the wavelength shifts
towards the red end of the spectrum.
 This is called red shift.
© Oxford University Press 2011
IP1.31.3 Light and the doppler effect
Spectral absorption
lines
 When we look at light
from stars and galaxies
there are some dark
lines found in the
spectrum of colour.
These dark lines mean
some wavelengths of
light are missing.
 These lines are called
spectral absorption
lines. The missing
wavelengths have
been absorbed by the
atoms in the star.
© Oxford University Press 2011
IP1.31.3 Light and the doppler effect
Spectral absorption lines and red shift
 When you look at distant galaxies they don’t actually seem redder.
The speed of light is too fast for us to be able to see a colour change.
 We see red shift as a movement of spectral absorption lines.
 The dark lines should always appear in the same place, as the atoms
can only absorb certain wavelengths.
 When we look at spectral absorption lines for distant galaxies the
lines are shifted towards the red end of the spectrum. This is
because the galaxy is moving away from us.
 Scientists found that the further away a galaxy is, the greater this
shift. In other words the galaxies further away are moving faster.
© Oxford University Press 2011
IP1.31.3 Light and the doppler effect
Edwin
Hubble, an
American
physicist,
was the first
to notice red
shift in distant
galaxies. The
fact that
distant
galaxies are
moving faster
is called
Hubble’s
Law.
© Oxford University Press 2011