In my Misconceptions, part 1 post I included as an example the common misconception:
Seasons are caused by the variation in the distance between the sun and Earth. When Earth is closer, we experience summer, and when it is further away, we experience winter.
Why do students come to the classroom with this misconception? Firstly, the most common image students see that describe the earth orbiting the sun is this one:
In fact, grab a science textbook near you and see if you have this figure. Go ahead, I’ll wait.
Now, try to find a statement about the shape of the orbit of the earth. If you spent some time with your handy textbook, would you know that the earth’s orbit was nearly circular? It doesn’t help that we call the orbit of the earth around the sun an “ecliptic”, which sounds a lot like “elliptic”. (You might ask, “why do textbooks use this figure?” I’ve heard it is to save space, and because the purpose isn’t to show the orbit of the earth – but retention-wise, this diagram does cause problems, particularly for students who are visual learners.)
Imagine you are an elementary aged student. Based on your experience, would you conclude that the earth is closest to the sun in summer when it is hot, and furthest in winter when it is cold? Probably. In fact, after encountering the diagram above, you might revise your understanding about the orbit of the earth to this (in the figure below, winter and summer are labeled correctly with Earth being closer to the sun in winter, but a student might assume that’s a typo):
These ideas, because they start in such young minds, are often more strongly held than new ideas. Further, its possible that many kids take this as truth, and its hard to overcome these misconceptions.
Check out this video. Its about 20 minutes long, but worthwhile.
So, how can we teach this so students better retain accurate information?
Firstly (and particularly with my pre-service teachers) I show them everything I’ve shown you here. We discuss what experience we have that tells us about the seasons and the orbit of the earth. We look for figures in our texts that show the orbit, and we analyze what the figures are trying to show (and point out when they are not intending to teach us the shape of the orbit). We then come up with as much information as we can, including:
- We have patterns of day and night (indicating the earth is rotating in addition to revolving)
- The sun and stars move across the size, in a consistent way (the earth is rotating). Further, their location changes slightly through the year.
- The southern hemisphere has the opposite season from the northern hemisphere (refuting the idea that the distance between the earth and sun drives the seasons).
For the younger set – we do lots of modeling and playing. Also, I teach the concept by using accurate figures. I only draw circular orbits on the board. Period. If you are using a worksheet, use one with circular (and not squashed) orbits.
Next, you will need some balls and flashlights. I particularly like to use inflatable globes. Keep in mind that planetary motion is a difficult concept (even for some adults and Harvard graduates).
1. Investigate the day and night periods on Earth caused by rotation. Have one student stand in for the sun by holding a flashlight (the bigger, the better) and shine it on your Earth model. Observe that the side facing the sun has “day” while the side away has “night”. Whoever is holding Earth can even spin it so that you can see the day/night period change for a single place. (Almost all students get this right. Its great for confidence at the start of the lesson.)
2. Show how we get phases of the moon. (This is harder. Model carefully.) The sun and Earth do not move, have a third student hold a sphere to represent the moon. The moon then moves around the Earth. Students may observe that the moon is usually half lit/half dark like Earth, but to see the phases of the moon we have to consider how the moon looks from a fixed position on Earth. I usually have a good chunk of a class challenge this (or just look at me like I’m insane) so in a short period of time either all the students are standing around my model (the people holding flashlights and orbs) or they want their own set to play with. Its nice when we have lots of flashlights and various balls to use to show these ideas. I think this is important for my pre-service teachers course – I want them to be able to use real science terms to explain complex ideas to each other, so we practice in the safe place of our classroom.
3. Once everyone has a firm grasp of planetary (and lunar) motion, we can talk about seasons. Earth’s axis of rotation is tilted, so the sun has a different effect on different parts of the globe.
Draw a simple diagram on the board (show a slide, teacher’s choice) of the earth, tilted on its axis. Draw a few arrows, all parallel to the floor: one hitting the pole, one near the equator, and one in between. Indicate that light reflects off Earth just as it reflects off the moon (and draw arrows). Now, help students understand that the opposite pole will not get sunlight for parts of the year. This sets up in their minds that there are places that are cold because they get no radiation from the sun. Other places (like the equator) get regular sun year round, and those places stay hot all the time. The poles, then, never really get warm because when they do get radiation, it can bounce off at a low angle (advanced students may also understand the idea of albedo – that all the snow and ice at the poles contributes to this effect as well).
When I do this series of activities with preservice teachers, it takes between 3 and 4 hours. For elementary kids, I would plan to work on this a bit each day for a week. Assessment that works well (for any age group, really) is watching them model for each other, having them sketch their own diagrams of planetary motion, and asking them to draw and explain the phases of the moon from the perspective of a person on Earth.