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PX268 Stars

Lecturer: Don Pollacco

Weighting 7.5 CATS

People have been studying stars for as long as anything else in science. Yet the subject is advancing faster now than almost every other branch of physics. With the arrival of space-based instruments, the prospects are that the field will continue to advance and that some of the most exciting discoveries reported in physics during your lifetime will be in astrophysics.

The module deals with the physics of the observation of stars and with the understanding of their behaviour and properties that the observations lead to. The module covers the main classifications of stars by size, age and distance from the earth and the relationships between them. It also looks at what the observations of stars' behaviour tell us about the evolutionary history of galaxies and of the Universe as a whole.


The module should introduce the methods used to measure the distances between stars, their brightness and colour and provide evidence for the large variability of stars found in our Galaxy. It should show how fundamental concepts of physics are used to quantitatively describe the structure and evolution of stars. The module should also explain how observational methods, such as imaging and spectroscopy, can be used to test our understanding of the origin, life, and death of stars.


At the end of the module, you should be able:

  • to define the position of a star
  • to describe the techniques used to determine their distance from us
  • to relate basic quantities such as apparent magnitude, absolute magnitude, flux, luminosity, stellar radius, effective temperature and distance.
  • To explain the main characteristics of stellar spectra along the main sequence
  • to understand the basic mechanisms of interaction between photons and matter occurring in the atmosphere of a star.
  • to understand the basic physical principles necessary to describe the structure and evolution of stars, and to qualitatively describe the birth, life and death of stars.
  • to be able to describe the processes of nuclear fusion that powers the light of almost all stars.
  • to identify the main features of the Hertzsprung-Russell diagram.


  1. Observational facilities - the optical/IR window - space based astronomy.
  2. Coordinate systems: how to define the position of a star. What stars are visible during a night, a month, a year.
  3. Trigonometric Parallax. The parsec and parallax angles. Statistical parallax.
  4. Fundamental properties of stars - colour, luminosity, apparent and absolute magnitude, stellar radius.
  5. Blackbody radiation, thermal equilibrium, effective temperature.
  6. Different types of stars - spectral classification - the Harvard spectral classification.
  7. Stellar atmospheres - where does the light that we observe originate - interaction between radiation and matter - radiation transfer.
  8. The sun: the best observed star. Solar cycle. Magnetic activity.
  9. The structure of stars -basic equations - nuclear energy production - mass/radius/luminosity relation - understanding the observed Hertzsprung-Russell diagram
  10. Stellar evolution - main sequence life time - from birth to death - young stellar objects, stellar remnants: white dwarfs, neutron stars, black holes.
  11. Using stellar populations as test beds for stellar evolution open and globular clusters.
  12. Exoplanets: discovery and characteristics. Equilibrium temperature and the habitable zone.

Commitment: about 18 Lectures

The questions on the problem sheets relate principally to the techniques presented in the module and working through them will help you to understand the material. Please feel free to approach me if you have any difficulties with the questions.

Assessment: 1 hour examination

This module has a home page.

Recommended Texts: B.W. Carroll and DA Ostlie, An Introduction to Modern Astrophysics, Addison-Wesley; Prialnik, D, An introduction to the theory of stellar structure and evolution., CUP.

Leads to: PX397 Galaxies, PX387 Astrophysics, PX389 Cosmology