State Hubble’s law. Identify any symbols that you use.
A star of luminosity 
is a distance of 
from the Earth. The star is in a distant galaxy. A spectral line in the light from this galaxy is known to have a wavelength of 
. This spectral line in the light from the galaxy observed on the Earth has a wavelength of 
.
Explain why the wavelength observed on the Earth is different from the wavelength that the galaxy is known to have emitted.
Determine a value for the Hubble constant 
.
is the recessional speed of the galaxy, 
is the distance of the galaxy from the observer, and 
.
