CTS Guide: Earth-Sun System, pp 236-237- Section IV Research Summaries
Sun-Centered System
Students’ grasp of many of the ideas about the composition and magnitude of the universe has to grow slowly over time. In spite of common depiction, the Sun-centered system seriously conflicts with common intuition (AAAS 2009).
Day-Night Cycle
Explanations of the day/night cycle, the phases of the Moon, and the seasons are very challenging for students. To understand these phenomena, students first should master the idea of a spherical Earth, itself a challenging task (AAAS 2009).
Danaia and McKinnon (2007) tested 1,920 middle school students in grades 7, 8, and 9 in Australia on a number of different astronomy tasks. The percentage of correct responses to a question about the causes of the day-night cycle was 19.5% in grade 7, 31.5% in grade 8, and 39.9% in grade 9. The most common misconceptions were that “The Earth orbits the Sun daily” or “The Sun goes around the Earth every day.” Although all students had learned about the motions of the Earth, the great majority of middle school students were confused about what went around what.
Because the explanation for the daily cycle of light and dark has traditionally been taught at the early elementary grades, some researchers have attempted to teach the concept as early as preschool (ages 5 and 6). However, they have had little success (Valanides, Gritsi, and Kampeza 2000).
As part of an evaluation of a high school astronomy course, Sadler (1998) tested 1,250 high school students on basic astronomical knowledge. About 66% of the students correctly answered the question “What causes night and day?” by choosing the response “The Earth spins on its axis.” Most of the students who failed the item chose “The Earth moves around the Sun.” What was most surprising was that as students learned more about astronomy, they were more likely to respond to this question by choosing a factually correct statement (“The Earth moves around the Sun”) even though it was the wrong answer to the question (about the cause of night and day). In other words, the more students learned about motions of the Earth, Sun, and Moon, the more confused they became—at least until they were able to straighten it all out. Sadler concluded, “New curricula should discuss and treat alternative concepts not as errors, but as stepping stones to scientific understanding” (p. 290).
Mant and Summers (1993) interviewed primary school teachers in England. Although most could explain the day/night cycle in scientific terms, few could relate their explanations to observations of how the Sun appears in the sky. Some appeared to work backward from their explanation to describe what must be happening in the sky. That suggests it is important to have students first observe how the Sun changes its position during the daytime, before explaining why that happens from the viewpoint of a spinning Earth.
Some students at the secondary level may still believe that day and night occur because Earth goes around the Sun or the Sun goes around Earth (Schoon 1992).
An older study by Baxter (1989) identified six ideas about day and night and showed that students, starting in preschool, seem to move through these ideas as they get older: (1) the Sun goes behind the hills, (2) clouds cover the Sun, (3) the Moon covers the Sun, (4) the Sun goes behind Earth once a day, (5) Earth goes around the Sun once a day, and (6) Earth spins on its axis once a day.
Sun’s Position and Apparent Motion in the Sky and Shadows
Plummer and Krajcik (2010) interviewed 60 students—20 each in grades 1, 3, and 8—about their ideas concerning how the Sun moves in the sky during the day. None of the first-grade students and only a few of the older students (20% in third grade and 10% in eighth grade) knew that the Sun does not pass directly overhead.
Plummer (2008) interviewed a total of 60 children in grades 1, 3, and 8, and developed a learning progression for realistic expectations for developing students’ ideas about the Sun’s motions: 1)For grades K–1 the Sun rises and sets, and it is in the sky during the daytime but not at night. 2) For grades 2–3 the Sun rises, moves continuously through the sky, and sets on the opposite side of the sky. 3) For grades 4–5 the Sun is highest at noon but does not pass directly overhead. Also for grades 4–5 the length of the Sun’s path and its highest point in the sky changes across the seasons.
A sample item from a set of astronomy diagnostic questions asks college students, “As seen from your location, when is the Sun directly overhead at Noon (so that no shadows are cast)? “ Common incorrect responses included every day; on the day of the summer solstice; on the day of the winter solstice; and at both of the equinoxes (spring and fall). Many college students failed to select the correct response: never from the latitude of your location (Zeilik, Schau, and Matter 1998).
Students seem to have more success in locating where an object’s shadow will fall in relation to a light source if the object is a person. They have more difficulty anticipating where a shadow will fall if it is a nonhuman object, such as a tree (Driver et al. 1994).
Relative Size of the Sun, Earth, and Moon
Mustafa (2007) interviewed students in Turkey who were approximately 14 years old, corresponding to ninth-grade students in the United States, concerning their ideas about the relative sizes of the Earth, Sun, and Moon. Of the 64 students interviewed, 28 (43%) knew that the Earth is smaller than the Sun and larger than the Moon; 10 of those who gave the correct answer (16% of the total number interviewed) could also say approximately how many times larger the Sun is than the Earth and the Moon. However, when the researcher asked the students to draw the Earth, the Sun, and the Moon, none of them attempted to show the correct scale; and when asked about the inconsistency, they were not able to explain. The author concluded that “the students may have memorized the size of the Earth, but their alternative frameworks remained unchanged” (p. 46).
Jones, Lynch, and Reesink (1987) interviewed 32 children from the third and sixth grades in Tasmania, asking them to pick out three-dimensional shapes and sizes to illustrate their understanding of the shapes and sizes of the Earth, the Sun, and the Moon. Only 25% of the children indicated that the Sun is larger than the Earth and that the Earth is larger than the Moon. Although there were no gender differences among the third graders, in sixth grade seven of the boys chose the correct order of sizes and only one girl chose the correct order.
Sadler (1987) interviewed 25 ninth-grade students about their ideas concerning the Earth, the Sun, and the Moon. About half of the students had just taken an Earth science course that included a major portion on astronomy. The students were asked to draw the Earth, the Sun, and the Moon. Nearly all of the students’ drawings showed the Earth, the Sun, and the Moon to be about the same size or within a factor of 2 of each others’ diameters—even though the Earth is 4 times the diameter of the Moon and the Sun is more than 100 times the diameter of the Earth.
Relative Distance Between Sun and Earth
Mustafa (2007) interviewed 64 students in Turkey about their understanding of the Earth, Moon, and Sun. The students were approximately 14 years old, corresponding to ninth-grade students in the United States. The students were asked: “If you used a basketball to represent the Sun, about how far away would you put a grape to represent the Earth?” Nineteen of the students (29%) had some knowledge of the Sun’s distance; either they knew that the Sun is 300–400 times farther from the Earth than the Moon or they had cor- rectly memorized the Sun’s distance to be 149,600,000 kilometers from Earth. How- ever, only one student correctly answered the question—that if the Sun is the size of a basketball, a grape that represents the Earth should be placed about 30 meters (98 feet) from the Sun.
Bakas and Mikropoulos (2003) gave a written questionnaire to 102 middle school students, ages 11–13, in Greece. They found that the majority of students (64%) understood that the Sun is much bigger than the Earth. However, only 16% were able to estimate the distance of the Earth from the Sun in a model in which the Sun is represented by an orange.
Sadler (1992) developed a written test to measure high school students’ understanding of astronomy concepts. An initial pilot of the test items with a small sample of students showed that approximately 80% of the students in grades 8–12 knew that the Earth is 93 million miles from the Sun, so a question asking how far Earth is from the Sun was thought to be too easy to use on the test. However, an item that was included in the test asked students to imagine a scale model in which the Sun is the size of a basketball, and to estimate how far from the basketball Earth should be located. The test was administered to 1,414 students in grades 8–12 who were just starting an Earth science or astronomy course. Responses were nearly equally distributed across choices of 5 feet, 10 feet, 25 feet, and 100 feet, indicating that memorizing the distance between the Earth and the Sun did not help students visualize the scale of the Earth-Sun system.
Sunspots
Neil Comins’s 2003 book Heavenly Errors: Misconceptions About the Real Nature of the Universe catalogs more than 1,700 misconceptions about astronomy gathered from his students at the University of Maine. Comins defines misconceptions as “deep- seated beliefs that are inconsistent with accepted scientific beliefs.” In his book he explores several misconceptions in detail, and offers explanations for why they occur. The following are a few of the misconceptions about sunspots from his website,www.physics.umaine.edu/ncomins: 1) Sunspots are hotter places on Sun, not cooler. 2) Sunspots are permanent (or are craters on) the Sun. 3) Sunspots are blemishes on photographs. 4) Sunspots are just “discolorations” to the Sun’s surface. 5) Sunspots are regions of soot on the Sun. 6) Sunspots are volcanic in origin. 7) Sunspots are holes on the surface of the Sun. 8) Sunspots are places on the Sun that have run out of fuel to burn. 9) Sunspots are spots on the skin darkened by the Sun.