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Essential idea: A simple diagram that plots the luminosity versus the surface temperature of stars reveals unusually detailed patterns that help understand the inner workings of stars. Stars follow well-defined patterns from the moment they are created out of collapsing interstellar gas, to their lives on the main sequence and to their eventual death.
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. (1.11)
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
Theory of knowledge:
The information revealed through spectra needs a trained mind to be interpreted. What is the role of interpretation in gaining knowledge in the natural sciences? How does this differ from the role of interpretation in other areas of knowledge?
Utilization:
An understanding of how similar stars to our Sun have aged and evolved assists in our predictions of our fate on Earth
Aims:
Aim 4: analysis of star spectra provides many opportunities for evaluation and synthesis
Aim 6: software-based analysis is available for students to participate in astrophysics research
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
Guidance:
Regions of the HR diagram are restricted to the main sequence, white dwarfs, red giants, super giants and the instability strip (variable stars), as well as lines of constant radius
HR diagrams will be labelled with luminosity on the vertical axis and temperature on the horizontal axis
Only one specific exponent (3.5) will be used in the mass–luminosity relation
References to electron and neutron degeneracy pressures need to be made
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