past paper notes- cosmology and astronomy

Question 1

Explain how cosmologists use observations of emission spectra from stars in distant galaxies to determine that the universe is expanding? /2

Answer 1

wavelengths of spectral lines are greater than their known values

redshift shows that stars in distant galaxies are moving away from Earth

Question 2

Explain how hubble’s law and the idea of the expanding universe lead to the big bang theory of the origin of the universe? /3

Answer 2

parts of the universe are moving away from each other

more distant objects are moving away faster

matter must have been close together in the past

Question 3

Explain how the surface temperature of a distant star may be determined from the wavelength spectrum of the light from the star? /3

Answer 3

wavelength of peak determined from spectrum of star

wavelength of peak intensity from object of known temperature determined

wien’s displacement law used