O: Astrophysics

Astrophysics (according to NASA) is the study of how the universe began, works and has evolved, and the search for life on planets around other stars. It's an ever-changing field as human manipulation of technology improves year on year. On 11th April 2019, for example, the first ever photograph of the event horizon of a black hole at the centre of a galaxy was captured.

The IB Physics course contains three key sections at Standard Level:

  • Stellar quantities (2 pages) - distinguishing between celestial bodies and defining units of length and brightness to cope with the vast magnitudes at play among the cosmos
  • Stellar characteristics and stellar evolution (4 pages) - categorising stars by examining the light they emit and using this information to diagnose a star's position in its lifecycle
  • Cosmology (2 pages) - using obervational evidence to make predictions about the past and future of the universe

The Advanced Higher Level topics are stellar processes and further cosmology.



  • Objects in the universe

    Objects in the universe, including galaxies, planetary systems and stars.

  • Stellar quantities

    The distances between objects in the universe and their brightness.

  • Spectra

    We can perform detective work on stars using their spectrum to determine temperature and chemical composition.

  • Stellar characteristics

    Stars can be displayed on a diagram and categorized in a number of ways.

  • Cepheid variable stars

    Cepheid variable stars, a pulsing star following the red giant stage, act as standard candles.

  • Stellar evolution

    The evolution of a star can be shown on the HR diagram.

  • Cosmology

    Scientists theorize that the universe commenced with a 'Hot Big Bang' of energy and matter. This theory is supported by evidence.

  • Age of the universe

    We can calculate an estimate for the age of the universe based on the velocity at which galaxies are receding from our observations.

  • AHL Stellar processes

    Having established the characteristics and evolution of different types of star, here we will dig a little deeper. Under what circumstances will a nebula collapse? What energy changes are happening during fusion beyond the main sequence? What happens to ma

  • AHL Further cosmology

    In the Cosmology and Age of the universe SL pages we considered cosmological observations and how these act as evidence for the origin and evolution of the universe in the past. Now we will instead look forwards to the future of the universe.