In this clip we see a portion of Scott Nelson’s elementary science curriculum in which students ponder the reason for seasons. Specifically, the students are responding to the following “challenge statement”, “If it’s summer in the United States, then why is it winter in Australia?”
Focus Practice: Modeling (SEP2)
To investigate this question, students discussed their initial ideas and conducted an investigation in which groups of students measured temperatures at different latitudes on a globe facing a fixed light source [see picture]. The class compiled each group’s data and used the findings as evidence to individually construct explanations to the challenge question.
After reading their responses, Scott was concerned that students were not accounting for the rotation of the Earth. So some students thought when a particular part of the Earth was facing away from the sun, it was winter. To address this issue he began the following day by representing the Earth/Sun system with a globe orbiting around a student representing the Sun. He then asked students to reconsider their explanations from the previous lesson.
Student's Model Ideas
After physically demonstrating the earth’s orbit around the sun, the students generated explanations to support why it was summer in the US.
1. Nora shared that it is summer in the US because “it’s hitting more of the US than of Australia.” She recognizes that the sun hits all parts of the earth, but she associates summer with the sun hitting a particular location “more” than another location.
2. Noah builds upon this idea to note that it is the angle at which the sunlight hits the Earth that leads to sunlight “hitting” particular locations “more” (“[It’s] summer and winter depending on the angle of which it’s being hit. So if the sun is Evan, and it’s hitting more of the US now, then it would be hotter making it summer.”)
3. Noah further explains that when the earth “fully rotates” around the sun, then Australia now has summer and the US has winter. Thus, he recognizes the seasons correspond to the Earth’s position around the sun, which influences the angle at which it receives sunlight.
These are model ideas because they are general principles that students can apply to explain how and why we have a particular season at any geographical location or position in the orbit around the sun. One student in particular wanted to see how the developing model could be used to explain what season the US would be “in the middle” of the orbit.
Two Earths, One Sun Scenario
Building on Noah’s ideas that angle and orbit position influence the seasons, Scott setup two globes on opposing sides of its orbit around the sun (see photo below). Recognizing students’ prior confusion about the earth’s rotation around the sun, he had the US facing the sun at each position. He had the student notice the angle at which the US was facing the sun and posed the question, “Which globe represents summer in the US?” Thus, Scott asked the students to test their model by using it to figure out which position represented summer for the US.
Each of the three students replying to Scott’s question agreed that the left globe represented summer in the US. However, they differed in their rationales.
Adrian noted that the US was “closer” to the Sun, which prompted the teacher to ask whether anyone disagreed with Adrian’s idea.
Nora built upon Adrian’s descriptor of “closer” by noting that the US was “closer to the axis” or “equator.” Scott attempted to clarify the language used to describe this point of reference as the “center of the earth” to be consistent with the investigation and note that the location of the US with respect to the equator does not change. She then references data from the experiment to support her idea that “it would be hotter when it’s in the center of the earth rather than at the top or the bottom.”
Noah specifically addressed Adrian’s use of the term “closer” by noting that the distance between the earth and sun is the same at both points (“It’s directly in the middle. The sun would not be closer or further to either one.”) The only thing that’s different is the angle, which he describes as whether the US is “facing down” or “facing up” more. Adrian then clarifies his initial statement by noting that his use of “closer” was consistent with Nora’s idea that summer in the US is due to it being “lower, so the sun affects it more.”
Watch the classroom video from Scott's perspective as he explains his decisions and highlights features and things for teachers to notice when supporting students’ engagement in modeling.
Scott gave the rest of the students the opportunity to evaluate the ideas against the evidence from investigation. Students are asked to consolidate their ideas in small groups.