How far is far? Investigating students’ knowledge about distance to astronomical objects

Title: Cross-sectional study of students’ knowledge of sizes and distances of astronomical objects
Authors: Vinesh M. Rajpaul, Christine Lindstrøm, Megan C. Engel, Morten Brendehaug, and Saalih Allie
First author institution: University of Cambridge
Journal: Physical Review Physics Education Research, 14 020108 (2018)

Unlike much of introductory physics which deals with everyday scales, most of the scales in astronomy are beyond the human experience. Indeed, the largest distance that a typical human has experienced, the circumference of Earth encountered during long flights, is only a tenth of the distance to the nearest celestial body, the Moon. Further, most humans only see the universe from the surface of earth, where the Moon looks to be the same size as the Sun, both of which look much bigger than the planets and stars. Perhaps it is no surprise then that investigating what students think about the size of and distance to celestial objects has been an area of interest for the Astronomy Education Research (AER) community. While most of the research into this area has focused on objects within the Solar System, today’s paper extends the research into the universe as a whole. Specifically, the authors of today’s paper were interested in prevalent incorrect views about the size and distances between objects both inside and outside of the Solar System and how those incorrect views may be different among students at different education levels.

First, some background. While there have been multiple studies investigating what students think about the size of various Solar System objects (such as this one and this one), it is hard to compare the results of the studies because the results are strongly linked to how the questions are asked. For example, one study found that nearly twice as many students could select the correct Moon-Earth distance from a list as could select a correct scale model of the Moon and Earth with the correct distance. Further, for comparing the size or distance of multiple objects, multiple choice questions can only provide a limited subset of the possible responses and hence, most studies only include 2 or 3 objects.

To build off the previous work and to compare different levels of students, the researchers administered three questions on the Norwegian Introductory Astronomy Questionnaire (NIAQ) to multiple levels of students. The questions used in this study are shown in figure 1.

Figure 1: Questions from the NIAQ used in this study (English version). These questions correspond to items 5a, 5b, and 7 respectively

The researchers then administered the questionnaire to year 8 (N=535) and year 10 (N=387) middle school students at multiple middle schools in Oslo, Norway and to pre-service science teachers enrolled in a second semester science course covering astronomy topics at Olso and Akershus University College of Applied Sciences, the largest teacher education institution in Norway. The pre-service teachers’ performance on the questionnaire was compared before and after completing their science course while the year 8 students who had never had astronomy covered in their courses were used as a pre-sample while the year 10 students who did have astronomy while in year 8, were used as the post-sample to eliminate any instructor-effects.

So what did the researchers find? First, when asked to rank a galaxy, a planet, a star, the universe, and a solar system in size, neither the students nor the pre-service teachers showed improvement in their ranking ability after instruction (72.5% to 69.6% pre-post students, and 90.5% to 91.6% pre-post for teachers, figure 2). The most common incorrect answer during this ranking task was that a planet was bigger than a star (40% students thought this on the pre-test and post-test) and that a solar system is larger than a galaxy (15%-20% of students on the pre- and post-test). These incorrect answers were still present in the post-test responses of pre-service teachers, but less than 10% of them gave these type of responses.

figure 1
Figure 2: Distribution of scores on question 1: ranking the size of a star, planet, galaxy, solar system, and universe. (Figure 1 in paper).

On the second question, the researchers found that both the students and the teachers could best provide what is meant by the terms solar system and universe compared to planet, star, or galaxy. The students did not show significant differences in ability to describe the terms between pre- and post-testing while the pre-service teachers showed improvements on all five terms.

On the third question, the researchers again found that the students showed no statistical difference in performance on the pre- and post-test (35.3% to 37.3% correct) while the pre-service teachers did (52.8% to 64.8% correct). Full results are shown in figure 3.

figure 4
Figure 3: Distribution of the scores on question 3: ranking the distance of ten objects from the surface of Earth. (Figure 4 in paper).

The most common mistakes were to rank the ozone layer as farther than the center of the Earth from the surface of the Earth and to believe the pole star Polaris, is closer to Earth’s surface than the edge of the Solar System is, suggesting that Polaris resides in the Solar System. Interestingly, 50% of students (post-instruction) thought the ozone layer was farther from Earth’s surface than the center of Earth was while 20% of pre-service teachers made this mistake post-instruction. The percentage of students and teachers believing Polaris was closer to Earth’s surface than the edge of the Solar System was approximately the same.

After analyzing the individual questions, the researchers looked for patterns in the responses between questions. It is often assumed that students need to understand size and distance before they can understand astronomical phenomenon: for example, the planets orbiting the Sun seems more reasonable if the Sun is bigger than the planets as opposed to the planets being bigger than the Sun. If this were the case the researchers reasoned, then students and teachers who were able to describe what galaxies, solar systems, and planets are (question 2) should have also performed well on the ranking task (question 3). Indeed, the researchers found that the more knowledgeable the students were about the objects, the more likely the student was to have the proper distance relation between the objects. As an example, of students who could not describe what a planet or a star were, only 54% of them were able to determine that a star was bigger than a planet while of the students who could describe what a planet and a star were, 98% of them knew that a star was bigger than a planet.

So what can we take away from this paper? First, even after instruction, many students and pre-service teachers have incorrect conceptions of the distance to various astronomical objects. Specifically, many students believe that planets are bigger than stars while both students and pre-service teachers believe that stars other than the sun lie within the Solar System. Given that nearly half of students and a quarter of the teachers answered in this manner post-instruction, the belief seems to be strongly held and highly resistant to change.

Second, having qualitative knowledge about the astronomical objects implies the student has ranking knowledge about those objects but the converse is not true. That is, students can rank the relative distances of objects without having an understanding of those objects.

Finally, instruction does not seem to remedy these mistakes. Instead, the authors recommend that instructors explicitly reconcile the textbook knowledge with the experiential knowledge students already have from looking up at the sky. The authors suggest the use of simulations or visualizations as well as analogies that map the astronomical scales to more familiar ones.

Figures used under Creative Commons Attribution 4.0 International license. Header image used under Creative Commons Attribution-Share Alike 3.0 Unported license. Image link

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