5.5  Astrophysics and Cosmology


5.5.1  Stars

Learners should be able to demonstrate and apply their knowledge and understanding of:


(a) the terms planets, planetary satellites, comets, solar systems, galaxies and the universe



(b) formation of a star from interstellar dust and gas in terms of gravitational collapse, fusion of hydrogen into helium, radiation and gas pressure Learners are not expected to know the details of fusion in terms of Einstein’s mass-energy equation.


(c) evolution of a low-mass star like our Sun into a red giant and white dwarf; planetary nebula



(d) characteristics of a white dwarf; electron degeneracy pressure; Chandrasekhar limit



(e) evolution of a massive star into a red super giant and then either a neutron star or black hole; supernova


(f) characteristics of a neutron star and a black hole



(g) Hertzsprung–Russell (HR) diagram as luminosity-temperature plot; main sequence; red giants; super red giants; white dwarfs.




5.5.2  Electromagnetic radiation from stars

Learners should be able to demonstrate and apply their knowledge and understanding of:


(a) energy levels of electrons in isolated gas atoms



(b) the idea that energy levels have negative values


(c) emission spectral lines from hot gases in terms of emission of photons and transition of electrons between discrete energy levels


(d) the equations  



(e) different atoms have different spectral lines which can be used to identify elements within stars



(f) continuous spectrum, emission line spectrum and absorption line spectrum



(g) transmission diffraction grating used to determine the wavelength of light



(h) the condition for maxima  , where d is the grating spacing.

Proof of this equation is not required.



(i) use of Wien’s displacement law  to estimate the peak surface temperature (of a star)



(j) luminosity L of a star; Stefan’s law



(k) use of Wien’s displacement law and Stefan’s law to estimate the radius of a star





5.5.3  Cosmology


Learners should be able to demonstrate and apply their knowledge and understanding of:


(a) distances measured in astronomical unit (AU), light-year (ly) and parsec (pc)



(b) stellar parallax; distances the parsec (pc)


(c) the equation     where p is the parallax in seconds of arc and d is the distance in parsec



(d) the Cosmological principle; universe is homogeneous, isotropic and the laws of physics are universal



(e) Doppler effect; Doppler shift of electromagnetic radiation



(f) Doppler equation   for a source of electromagnetic radiation moving relative to an observer



(g) Hubble’s law;  for receding galaxies, where H0 is the Hubble constant



(h) model of an expanding universe supported by galactic red shift



(i) Hubble constant   H0 in both km s-1 Mpc-1 and s-1  units




(j) the Big Bang theory



(k) experimental evidence for the Big Bang theory from microwave background radiation at a temperature of 2.7 K  The development and acceptance of Big Bang theory by the scientific community.



(l) the idea that the Big Bang gave rise to the expansion of space-time


(m) estimation for the age of the universe; 



(n) evolution of the universe after the Big Bang to the present



(o) current ideas; universe is made up of dark energy, dark matter, and a small percentage of ordinary matter.