October 09, 2021 Filed in: Articles

Back in the day, I used to teach at the Ontario Science Centre and present their school programs. I would meet the visiting teacher and mob of grade 9 students in advance of my “Cosmic Connections” program and ask, “So has your class covered the astronomy unit yet?” On more than one occasion, the teacher answered, “No. You’re it!” That’s right; my 45-minute extravaganza was all the astronomy that students would get in grade 9. Despite fifteen years passing since then, the topic of astronomy still does not fall within every teacher’s comfort zone, so I hope that sharing the resources for our inquiry-based unit on grade 9 astronomy will help. In this article I will explain the ideas and pedagogical design of our unit and hopefully encourage you to check it out!

Diagrams are a powerful tool for representing and understanding what we see in the sky. We start by introducing polar diagrams of the sky and sun path diagrams, showing the position of the Sun in the sky at different moments during one day. Here are PowerPoint slides from the Astronomy Course Guide showing these diagrams:

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We can also create a polar diagram for the Moon and track its “movement” across the sky too!

Another tool we use is the Sun-Earth-Moon System diagram. This shifts the point of view from the Earth (like in the sun path diagrams) to the “fixed stars” looking down on the solar system and Earth’s north pole. It allows us to visualize the Earth and Moon at different times and predict what Moon phase would be visible. The dot on Earth represents an observer.

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Students need to understand that most of the drawings we make of the sky and solar system are not in correct proportions: if the distances between objects are, the diameters are usually not; and vice versa. If both are, you probably have a diagram or representation that does not fit on any page. Despite this challenge, understanding the correct proportions is an important part of making sense of space!

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Scientific notation allows for very quick comparisons of size and reduces the “you missed a zero” error. Students will need explicit guidance on how to use their calculators:

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A common student mistake is typing in: 1.27 x 10 x

13.8 billion years ↔ 13.8 x 10

Did you notice I kept writing “years” with each example above? Numbers in science usually represent measurements and do not make sense when written without units, so train students to write a unit with every measurement number. To help students practice their number writing skills, we use a summary page for the exotic numbers we encounter in this unit.

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An important part of understanding the mathematical conversion process is showing that the original units divide away. This is what convinces us that we have set up the math work correctly. But to make sense of the result, students need to be prompted to reflect, and question #3 in the above example does exactly that. This is based on an important concept: converting to a smaller physical unit yields a larger number (more of those units).

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This is how we make sense of the conversion process: by understanding how the number part should change.

b) Hours to years?

c) Light years to astronomical units? Whoa, getting ahead of ourselves!

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Notice all the structure that guides students’ mathematical work and sense-making. They will not do this unless you insist on it every time! In this example, students are trying to choose an object to best represent Earth in correct proportions to a ball that represents the Sun. We continue the math work by thinking about how to use this ratio result and making sense of the mathematical challenge: should we multiply or divide with it? The full calculation process is carefully modeled (written out explicitly) and explanatory notes are given for each step. These notes will become the reminders students use when they complete a full calculation on their own.

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I find this level of structure is helpful for both the weak students and the strong ones (an example of universal design for learning). Many students who are comfortable with the math work don’t actually understand it or are terrible at thoughtfully explaining it. This structure forces them to think about what they are doing and describe it clearly. Since it is modeled so carefully, I don’t accept (i.e. award marks to) any work that has any significant errors or omissions.

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- Earth’s axial rotation, the Moon’s orbital rotation, and Earth’s orbital rotation
- Nope! We live further north beyond the tropic of cancer.
- Summer – a long sun path = many daylight hours, sunrise and sunset occur to the north
- Earth’s rotation about its axis, one day!
- Many! The diameters of the object are out of proportion (Sun too small, Moon too big) and the distances are off (Earth too close to Sun, Moon to close to Earth)
- It is a bit before midnight, closer to sunset.
- Roughly half, maybe a bit more shaded than lit.
- How long did it take you? Did you find the first one sufficiently annoying?
- The number part gets bigger, smaller, bigger.