Syllabus outcomes:
8.5.3.3.1 Gather secondary information to relate brightness of an object to its luminosity and distance
8.5.3.3.2 solve problems to apply the inverse square law of intensity of light to relate the brightness of a star to its luminosity and distance from the observer
Students will learn to:
Students will learn what affects star brightness and represent the inverse square law on a graph.
Prior knowledge:
8.5.3.2.2 Identify that the surface temperature of a star is related to its colour
8.5.3.2.4 Identify energy sources characteristic of each star group, including Main Sequence, red giants and white dwarfs
8.5.3.2.3 Describe a Hertzsprung-Russel diagram as the graph of a star’s luminosity against its colour or surface temperature
Activity:
First, read this information page by the CSIRO about how brightness of stars relates to the distance, the "inverse square law".
8.5.3.3.1 Gather secondary information to relate brightness of an object to its luminosity and distance
8.5.3.3.2 solve problems to apply the inverse square law of intensity of light to relate the brightness of a star to its luminosity and distance from the observer
Students will learn to:
Students will learn what affects star brightness and represent the inverse square law on a graph.
Prior knowledge:
8.5.3.2.2 Identify that the surface temperature of a star is related to its colour
8.5.3.2.4 Identify energy sources characteristic of each star group, including Main Sequence, red giants and white dwarfs
8.5.3.2.3 Describe a Hertzsprung-Russel diagram as the graph of a star’s luminosity against its colour or surface temperature
Activity:
First, read this information page by the CSIRO about how brightness of stars relates to the distance, the "inverse square law".
Now, go to the Virtual Luminosity Simulator. Choose two of the light sources, note down their luminosity. Choose 5 points of distance and watch them being plotted on a graph. Now, copy down two of the graphs in your book and compare them.
Questions:
How could you mathematically express the relationship between them?
How does distance affect the flux? What is the formula that is used to calculate it?
Choose a luminosity double or half that of one of your graphs. Predict the flux at the distances equal to those in your graph.
Graph it using the simulator. Was your prediction correct?
Rationale:
This exercise introduces a mathematical explanation of how star brightness and distances are related. Again, this is based on a type of flipped classroom scenario and draws on constructivist methods of instruction that lets the teacher guide and scaffold the students' learning (Cunningham & Duffy, 1996). The use of the simulator lets students themselves explore visually the mathematical relationship that they've just read about, and apply the knowledge they've gained in interpreting the graph results. Rather than doing mathematical exercises, this activity lets students compare their calculation and knowledge to a graph determined from a simulated star and thus relates what could be an abstract concept into much more familiar and personal experience - looking at bright and less bright stars. This also is a cornerstone of constructivist instruction (Vygotsky, 1987).
References:
Cunningham, D., & Duffy, T. (1996). Constructivism: Implications for the design and delivery of instruction. Handbook of research for educational communications and technology, 170-198.
Vygotsky, L. (1987). Zone of proximal development. Mind in society: The development of higher psychological processes, 52-91.