D. Astrophysics
D. Astrophysics
Core
D.1 – Stellar quantities
Nature of science:
Reality: The systematic measurement of distance and brightness of stars and galaxies has led to an understanding of the universe on a scale that is difficult to imagine and comprehend.
Understandings:
Objects in the universe
The nature of stars
Astronomical distances
Stellar parallax and its limitations
Luminosity and apparent brightness
Applications and skills:
Identifying objects in the universe
Qualitatively describing the equilibrium between pressure and gravitation in stars
Using the astronomical unit (AU), light year (ly) and parsec (pc)
Describing the method to determine distance to stars through stellar parallax
Solving problems involving luminosity, apparent brightness and distance
D.2 – Stellar characteristics and stellar evolution
Nature of science:
Evidence: The simple light spectra of a gas on Earth can be compared to the light spectra of distant stars. This has allowed us to determine the velocity, composition and structure of stars and confirmed hypotheses about the expansion of the universe.
Understandings:
Stellar spectra
Hertzsprung–Russell (HR) diagram
Mass–luminosity relation for main sequence stars
Cepheid variables
Stellar evolution on HR diagrams
Red giants, white dwarfs, neutron stars and black holes
Chandrasekhar and Oppenheimer–Volkoff limits
Applications and skills:
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
Identifying the main regions of the HR diagram and describing the main properties of stars in these regions
Applying the mass–luminosity relation
Describing the reason for the variation of Cepheid variables
Determining distance using data on 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
D.3 – Cosmology
Nature of science:
Occam’s Razor: The Big Bang model was purely speculative until it was confirmed by the discovery of the cosmic microwave background radiation. The model, while correctly describing many aspects of the universe as we observe it today, still cannot explain what happened at time zero.
Understandings:
The Big Bang model
Cosmic microwave background (CMB) radiation
Hubble’s law
The accelerating universe and redshift (z)
The cosmic scale factor (R)
Applications and skills:
Describing both space and time as originating with the Big Bang
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
Estimating the age of the universe by assuming a constant expansion rate
Additional higher level
D.4 – Stellar processes
Nature of science:
Observation and deduction: Observations of stellar spectra showed the existence of different elements in stars. Deductions from nuclear fusion theory were able to explain this.
Understandings:
The Jeans criterion
Nuclear fusion
Nucleosynthesis off the main sequence
Type Ia and II supernovae
Applications and skills:
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
Describing the formation of elements in stars that are heavier than iron including the required increases in temperature
Qualitatively describe the s and r processes for neutron capture
Distinguishing between type Ia and II supernovae
D.5 – Further cosmology
Nature of science:
Cognitive bias: According to everybody’s expectations the rate of expansion of the universe should be slowing down because of gravity. The detailed results from the 1998 (and subsequent) observations on distant supernovae showed that the opposite was in fact true. The accelerated expansion of the universe, whereas experimentally verified, is still an unexplained phenomenon.
Understandings:
The cosmological principle
Rotation curves and the mass of galaxies
Dark matter
Fluctuations in the CMB
The cosmological origin of redshift
Critical density
Dark energy
Applications and skills:
Describing the cosmological principle and its role in models of the universe
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
Describing qualitatively the cosmic scale factor in models with and without dark energy
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