(a)[3]
Describe what occurs in the core of a stable star to release energy that is later transferred into space.
(b(i))[2]
Describe how the observed light differs from the light when it was emitted.
(b(ii))[1]
State the quantity that astronomers use to work out the speed at which the galaxy is moving away.
(c(i))[2]
Calculate the distance from the Earth of a galaxy that is receding at a speed of $1.3 \times 10^7$ m/s.
(c(ii))[2]
Calculate an estimate of the age of the Universe. Express your answer in years.