Unit Planner: Astrophysics

Unit: Astrophysics

Start date:

End date:

Diploma assessment

When will the content be assessed?

Paper 1
Paper 2
Paper 3 x
Investigation x

Text book reference

Hamper - online resources

Inquiry: Establishing the purpose of the unit

Transfer Goals
List here one to three big, overarching, long-term goals for this unit. Transfer goals are the major goals that ask students to “transfer”, or apply, their knowledge, skills, and concepts at the end of the unit under new/different circumstances, and on their own without scaffolding from the teacher.

  • To know the definitions of stellar quantities and stellar characteristics
  • To understand the process of stellar evolution
  • To be able to explain the evidence for current theories in cosmology

List here the key content that students will know by the end of the unit

Stellar quantities

  • Objects in the universe
  • The nature of stars
  • Astronomical distances

Stellar characteristics and evolution

  • Hertzsprung–Russell (HR) diagram
  • Mass–luminosity relation for main sequence stars
  • Red giants, white dwarfs, neutron stars and black holes


  • The Big Bang model
  • Cosmic microwave background (CMB) radiation

Stellar processes

  • The Jeans criterion
  • Type Ia and II supernovae

Further cosmology

  • The cosmological principle
  • Dark matter
  • Fluctuations in the CMB
  • Dark energy

List here the key skills that students will develop by the end of the unit.

Stellar quantities

  • Qualitatively describing the equilibrium between pressure and gravitation in stars
  • Using the astronomical unit (AU), light year (ly) and parsec (pc)
  • Solving problems involving luminosity, apparent brightness and distance

Stellar characteristics and evolution

  • Explaining how surface temperature may be obtained from a star’s spectrum
  • Explaining how the chemical composition of a star may be determined from the star’s spectrum
  • Sketching and interpreting HR diagrams
  • Applying the mass–luminosity relation
  • Determining distance using data on Cepheid variables


  • Describing the characteristics of the CMB radiation
  • Explaining how the CMB radiation is evidence for a Hot Big Bang
  • Solving problems involving z, R and Hubble’s law

Stellar processes

  • Applying the Jeans criterion to star formation
  • Describing the different types of nuclear fusion reactions taking place off the main sequence
  • Applying the mass–luminosity relation to compare lifetimes on the main sequence relative to that of our Sun
  • Qualitatively describe the s and r processes for neutron capture
  • Distinguishing between type Ia and II supernovae

Further cosmology

  • Describing rotation curves as evidence for dark matter
  • Deriving rotational velocity from Newtonian gravitation
  • Describing and interpreting the observed anisotropies in the CMB
  • Deriving critical density from Newtonian gravitation
  • Sketching and interpreting graphs showing the variation of the cosmic scale factor with time

List here the key concepts that students will understand by the end of the unit

Stellar quantities

  • Stellar parallax and its limitations
  • Luminosity and apparent brightness

Stellar characteristics and evolution

  • Stellar spectra
  • Cepheid variables
  • Stellar evolution on HR diagrams
  • Chandrasekhar and Oppenheimer–Volkoff limits


  • Hubble’s law
  • The accelerating universe and redshift (z)
  • The cosmic scale factor (R)

Stellar processes

  • Nuclear fusion
  • Nucleosynthesis off the main sequence

Further cosmology

  • Rotation curves and the mass of galaxies
  • The cosmological origin of redshift
  • Critical density

Examples of real world practical applications of knowledge.

  • Identifying objects in the universe
  • Describing the method to determine distance to stars through stellar parallax
  • Identifying the main regions of the HR diagram and describing the main properties of stars in these regions
  • Describing the reason for the variation of Cepheid variables
  • Sketching and interpreting evolutionary paths of stars on an HR diagram
  • Describing the evolution of stars off the main sequence
  • Describing the role of mass in stellar evolution
  • Describing both space and time as originating with the Big Bang
  • Estimating the age of the universe by assuming a constant expansion rate
  • Describing the formation of elements in stars that are heavier than iron including the required increases in temperature
  • Describing the cosmological principle and its role in models of the universe
  • Describing qualitatively the cosmic scale factor in models with and without dark energy

Action: teaching and learning through Inquiry

Approaches to teaching
Tick boxes to indicate pedagogical approaches used.

Lecture x
Simulation x
Small group work (pairs) x
Hands on practical
Video x
Student centred inquiry x

Examples of how TOK can be introduced in this unit

  • A lot of astrophysics is based on the assumption that what happens here happens out there, is this reasonable? What choice do we have but to make this assumption?
  • The story of Galileo and his conflict with the church is an interesting TOK issue.
  • Why were ancient civilisations so interested in the movement of the planets?
  • This scale is based on an original attempt to classify the stars in terms of their brightness using the naked eye. It is very difficult to do this bu the ancient Greeks were quite good, have we lost the ability to make these sort of measurements?
  • Time and time again we use concepts that have been developed on the Earth (Doppler, absorption spectra etc.) to help us understand things that we can not experiment with.
  • With today's instruments we can classify stars quite precisely however original classification according to brightness was based on perception.
  • The whole idea of what was there before the big bang is an interesting concept. It would have been impossible to observe the big bang since there was no space or time to observe it from. So what was there? is this question even possible to contemplate.
  • The big bang does not agree with some religious beliefs but how do they explain the CMB and redshift of galaxies?

Examples of how NOS can be introduced in this unit.

  • Because the sun is the nearest star we can gather more information about it than any other star. If we assume all stars are basically the same then we know a lot about all stars. What if all the stars are different?
  • Some stars are a very long way away, how can we claim to know anything about them? 
  • The way we deduce that the different stars are simply the same stars but at different stages in their lives is interesting. We can not see a star growing old as it takes too long what we see is old stars and young stars but what if this wasn't true and they are simply different stars?
  • Our universe seems to be made up of a limited number of particles, were these the only particles that could have been created by a big bang or could the universe have been very different?
  • When CMB was first detected it was thought to be uniform but if the universe expanded uniformly then how did galaxies form? The COBE satellite detected variations but was this just because they were looking for them.
  • Most binaries are not seen as two rotating stars but simply one star with a varying brightness or varying spectrum. Can we ever know if they really are two stars?
  • Just because the luminosity of all close Cepheids is related to their period does that mean that the same relationship should hold for the distant ones too?
  • We can only see those parts of the universe that give out light, the rest (96%) is called dark matter. How can we model things that we can not detect?
  • Why do scientists give things funny names like WIMPs and MACHOs?

Tests, exams and marked labs


What went well
List the portions of the unit (content, assessment, planning) that were successful

What didn’t work well
List the portions of the unit (content, assessment, planning) that were not as successful as hoped

List any notes, suggestions, or considerations for the future teaching of this unit.

All materials on this website are for the exclusive use of teachers and students at subscribing schools for the period of their subscription. Any unauthorised copying or posting of materials on other websites is an infringement of our copyright and could result in your account being blocked and legal action being taken against you.