THE HERTZSPRUNG-RUSSELL DIAGRAM OF CARS: IS IT AN EFFECTIVE ANALOGY IN TEACHING STELLAR ASTRONOMY?

The National Research Council has outlined the importance for high school students to comprehend the evolution of stars and the processes that occur in stars. The aforementioned concepts are also typically taught in most introductory astronomy courses at the college level. The Hertzsprung-Russell (H-R) Diagram is typically taught to express and teach the relationship between luminosity or absolute brightness versus spectral type or surface temperature of stars.

A number of astronomy textbooks utilize the H-R Diagram of Cars as an analogical device to introduce the core concepts of the H-R Diagram for stars. The analogy was originally published in the introductory astronomy textbook “Horizons: Exploring the Universe” by Michael Seeds, and it has since been adopted by other astronomy educators as an analogical tool. To the best of the authors’ knowledge, no researchers have ever compiled real car weight and horsepower data in order to verify the accuracy of the analogy.

Weight and horsepower data was collected from Edmonds.com for over 250 model year 2011 vehicles. The data was imported into an Excel spreadsheet where it was organized on the basis of the category of vehicle. Once all of the data was plotted, a simple visual inspection was conducted to determine the usefulness and limitations of the analogy.

The H-R Diagram for Cars analogy works quite well since cars have a nearly fixed ratio of weight to horsepower. The ‘Main Sequence’ of cars forms a diffuse line, thus providing a good analogy for the Main Sequence of stars. However, there is a limitation to the analogy because there are no cars below the ‘Main Sequence’ of cars, thus preventing it from being extended to white dwarfs. However, this can be easily corrected by adding data for small to medium-sized farm tractors. .

Further research is needed in order to critique the effectiveness and usefulness of the H-R Diagram of Cars. Additional questions could be answered concerning the most appropriate way to use stellar astronomy analogies in the classroom and if they are effective learning tools for all students.