--- title: "Why does the moon change shape?" subtitle: "Year 7 Earth and space · The moon · Lesson 3" --- # Why does the moon change shape? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** The moon looks like a thin smile one week and a bright full disc two weeks later. Nothing about the moon itself has changed. :::teacher-note **In one sentence:** Students sequence the eight moon phases and explain them by the moon's position relative to the Earth and sun, rejecting the Earth's-shadow explanation (AC9S7U03, node 2, a hinge node). **Students should be able to say:** I can put the eight phases of the moon in order. I can explain the phases by the moon's position, not Earth's shadow. I can predict the phase seen from Earth for a given position. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **What causes the moon's phases?** ☐ The moon changing shape ☐ Earth's shadow covering part of the moon ☐ Clouds covering part of the moon ☐ How much of the moon's sunlit half we can see from Earth, as it goes round us My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** How much of the sunlit half we can see. The sun always lights half the moon; as the moon goes round the Earth, we see more or less of that half. Earth's shadow is only involved in a lunar eclipse. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: positions and phases :::keep-together ### Order **Put the phases in order, starting from new moon.** A. `Waning gibbous` B. `First quarter` C. `Full moon` D. `Waning crescent` E. `Waxing gibbous` F. `New moon` G. `Last quarter` H. `Waxing crescent` Correct order (letters): {{field-24}} ::: :::teacher-note **Answer:** see the program below ```science New moon Waxing crescent First quarter Waxing gibbous Full moon Waning gibbous Last quarter Waning crescent ``` ::: :::keep-together ### The shadow **At first quarter, where is Earth's shadow?** ☐ Pointing away from the sun, nowhere near the moon: half the moon is dark only because we see half of its lit side ☐ In front of the sun ☐ Covering half the moon ☐ Covering the whole moon ::: :::teacher-note **Answer:** Pointing away from the sun, nowhere near the moon: half the moon is dark only because we see half of its lit side ::: :::keep-together ### Full moon **At full moon, where is the moon?** ☐ Between the Earth and the sun ☐ On the far side of the Earth from the sun, so we see its whole lit half ☐ At a right angle to the sun ☐ Closest to the sun ::: :::teacher-note **Answer:** On the far side of the Earth from the sun, so we see its whole lit half ::: :::keep-together ### Phase or eclipse **In a lunar eclipse, a full moon goes dark and reddish for an hour or two. How is that different from the moon's phases?** ☐ A lunar eclipse happens at new moon, when the moon is dark ☐ An eclipse is the moon going through all its phases in an hour ☐ An eclipse is Earth's shadow falling on the moon, only at some full moons; the phases come from how much of the lit half we see, every month ☐ There is no difference: a lunar eclipse is just a very dark phase ::: :::teacher-note **Answer:** An eclipse is Earth's shadow falling on the moon, only at some full moons; the phases come from how much of the lit half we see, every month ::: ## Mix it up :::keep-together **Looking back at spinning and orbiting: about how many times does the Earth spin during one trip round the sun?** ☐ About 365 ☐ About 12 ☐ About 24 ☐ Once ::: :::teacher-note **Answer:** About 365 One spin is a day and a trip round the sun is about 365¼ days, so the Earth spins about 365 times each year. ::: ## name the phase The moon is placed for you and the view from Earth is hidden. Where is it compared with the sun? Name the phase. :::typical ## Elaborate: a month of evidence :::keep-together **A student sees a full moon on 1 March. On about what day of March will the next full moon be?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 30 About 29.5 days later: 30 or 31 March. ::: ::: :::wider ## Elaborate: the view from Japan :::keep-together **From Australia a waxing crescent is lit on the left. From Japan it is lit on the right. Why?** ☐ People in the Northern Hemisphere see the moon 'upside down' compared with us, so left and right swap ☐ The moon's phase is different in Japan ☐ Japan sees a different moon ☐ It's lit on the left everywhere ::: :::teacher-note **Answer:** People in the Northern Hemisphere see the moon 'upside down' compared with us, so left and right swap ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - The sun always lights **half** the moon. The **phase** is how much of that lit half we can see, which depends on where the moon is in its orbit. - New moon → waxing crescent → first quarter → waxing gibbous → full moon → waning gibbous → last quarter → waning crescent (about 29.5 days). - Phases are **not** caused by Earth's shadow. From Australia a waxing moon is lit on the left. ## Exit ticket :::keep-together **Why do we see a half-lit moon at first quarter?** {{lines-3}} ::: :::teacher-note **Answer:** The moon is a quarter of the way round its orbit, at right angles to the sun; we see half of its sunlit half. It isn't Earth's shadow. :::