(a)[2]
State Hubble’s law. Identify any symbols that you use.
(b)[2]
A star with luminosity $3.8 \times 10^{31}\,\text{W}$ lies $1.8 \times 10^{24}\,\text{m}$ from Earth. Calculate the radiant flux intensity at Earth from the radiation emitted by the star.
(c(i))[2]
The star in (b) is in a distant galaxy. A spectral line in the galaxy’s light is known to have wavelength $486\,\text{nm}$. When that same line is observed on Earth, its wavelength is $492\,\text{nm}$. Explain why the wavelength measured on Earth differs from the wavelength the galaxy is known to have emitted.
(c(ii))[3]
Find a value for the Hubble constant $H_0$.