Learning Objective
To understand how Edwin
Hubble provided evidence
showing the relative scale of
the Universe.
Learning Outcome
To be able to explain
Hubble’s observations and
how they relate to the scale
model of the Universe.
Success Criteria
Good if: you can recall Edwin Hubble’s observations of
distant objects in the sky.
Excellent when: you can explain some of these observations
using the idea of ‘red shift’.
Exceptional if: you can use Hubble’s Law to calculate the
recession velocity of a given object.
After The ‘Great Debate’
After resolving the ‘CurtisShapley’ debate. Hubble
measured the distance to
Cepheid variable stars in
the Andromeda Galaxy:
2.5 million light years!
Hmm...Much further
than I suspected! I also
noticed something
else…..
Moving Galaxies
Hubble’s observations showed that the light from
distant galaxies was ‘red-shifted’. This was due to the
‘Doppler Effect’.
Light from
Light from
the Sun
By Golly, just
look at that!
The dark lines in
the spectrum
on the right
hand side are
‘red shifted’.
distant galaxies
Explaining Doppler Shift
Recession Velocity
Hubble also noticed that the further away the galaxy,
the greater the red-shift. The greater the red-shift the
greater the speed of recession.
My startling conclusion was that
the further away the galaxy, the
faster is was moving. Amazing! It
also led me to develop what later
became known as Hubble’s Law.
After Me!
Hubble’s Law
The red-shift of distant objects is easy to measure therefore
the recession velocity can also be easily calculated.
We can use the recession velocity to calculate the distance to a
galaxy (or the velocity if the distance is known). This is known as
Hubble’s Law.
Speed of recession (m/s) = Hubble Constant (s-1) x distance (km)
The value of the Hubble Constant is 2x10-18 s-1 (this value is still
being researched).
E.g. A galaxy is 1.5 x 1020 km away. How fast is it moving?
Recession Velocity = Hubble Constant x 1.5 x 1020
= 2x10-18 x 1.5 x 1020 = 300 km/s
Learning Objective
To understand how Edwin
Hubble provided evidence
showing the relative scale of
the Universe.
Learning Outcome
To be able to explain
Hubble’s observations and
how they relate to the scale
model of the Universe.
Success Criteria
Good if: you can recall Edwin Hubble’s observations of
distant objects in the sky.
Excellent when: you can explain some of these observations
using the idea of ‘red shift’.
Exceptional if: you can use Hubble’s Law to calculate the
recession velocity of a given object.