The sun always lights half of the moon. As the moon goes round the Earth (29.5 days from new moon to new moon), we see more or less of that lit half: the phases. They are not caused by Earth's shadow.
The moon looks like a thin smile one week and a bright full disc two weeks later. Nothing about the moon itself has changed.
You have watched the moon's phases. This lesson explains them.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Practise: A few on your own, to check you have it.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: what causes the phases?
ExploreTry it on the board and compare what happens with your prediction.
Explore: send the moon round
Drag the moon round its orbit, or press Next phase or Play a month. Watch the lit half of the moon (from above) and what we see from Earth. Then press Show Earth's shadow: where is the shadow at a quarter moon?
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Take the moon through all eight phases.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: positions and phases
In your book: draw the Earth, the sun's direction and the moon at four positions. Shade the lit half of each moon and draw what we see from Earth.
Put the phases in order, starting from new moon.
Pieces (click to add)
Your program
PractiseA few on your own, to check you have it.
Mix it up
PractiseA few on your own, to check you have it.
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.
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Name the phase correctly for five moons.
Use the board. This ticks when you get there.
Elaborate TypicalUse the same idea in a new context.
Elaborate: a month of evidence
A student sees a full moon on 1 March. On about what day of March will the next full moon be?
Elaborate WiderUse the same idea in a new context.
Elaborate: the view from Japan
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EvaluateLook back at your first ideas and what changed.
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.
For teachers
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). About 22 minutes.
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.
Before class
A concept tutorial for introducing or revising the idea; it pairs well with the lamp-and-ball model (a student holds a ball at arm's length and turns round a lamp) and a moon diary. Set the width with ?width=minimum, typical (default) or wider.
The hinge misconception is that Earth's shadow causes the phases. The shadow button shows the shadow is far from the moon at quarters and crescents; at full moon, the board's note explains that the tilted orbit usually takes the moon above or below it (the next lesson).
Board notes: not to scale; seen from above the North Pole, with the moon going anticlockwise. "What you see from Earth" is drawn for the Southern Hemisphere (waxing lit on the left) unless view: north. The quiz places the moon at one of the eight positions and hides the view until the student answers.
Running the lesson
Engage: count how many chose Earth's shadow.
Explore: ask students to put the shadow on at first quarter.
Explain: the shadow question is the checkpoint; the parsons task checks the sequence.
The hard part (on purpose)
Letting go of Earth's shadow as the cause. When a student says the dark part is the shadow, ask where Earth's shadow points and where the moon is at a crescent.
When students get stuck
A student says the dark part of a crescent is Earth's shadow. Ask: Where does the shadow point? Where is the moon at a crescent? Fix: The shadow points away from the sun; a crescent moon is nearly between us and the sun, so we see mostly its dark side.
A student mixes up waxing and waning. Ask: Is the lit part growing (waxing) or shrinking (waning) after new moon? Fix: Growing until full, then shrinking.
Stretch and support
Stretch: Why can you sometimes see a full moon rising just as the sun sets?
Support: Give a circle diagram with the eight positions and blank moon faces to shade.
Where it leads
Next: eclipses (node 3), which need the shadow and the tilted orbit, then tides (node 5).
In class: the lamp-and-ball model; a month-long moon diary.
What each step is for
Engage: what causes the phases?: The shadow misconception is the hinge; students who hold it will choose 'Earth's shadow', and the board shows the shadow is nowhere near the moon at most phases.
Explore: send the moon round: Linking each orbit position to its appearance from Earth builds the position-based explanation.
Explain: positions and phases: Sequencing all eight and rejecting the shadow explanation with evidence is the precision the node needs.
Mix it up: The moon's month is easier to picture next to the Earth's own spin and year, which this question brings back.
name the phase: Predicting the phase from a position, many times with feedback, makes the model reliable.
Elaborate: a month of evidence: Reading the cycle's period from evidence connects the model to observation.
Elaborate: the view from Japan: Seeing the same phase lit on the other side from the Northern Hemisphere shows the phase depends on position, and the view depends on where you stand.
Now you can
Put the eight phases of the moon in order.
Explain the phases by the moon's position, not Earth's shadow.
Predict the phase seen from Earth for a given position.