A solar eclipse happens at new moon when the moon's shadow falls on Earth; a lunar eclipse at full moon when the moon passes through Earth's shadow. The moon's orbit is tilted about 5°, so most months the shadows miss: eclipses come in seasons about six months apart.
There's a new moon every month, with the moon between us and the sun. Yet the next total solar eclipse seen from Sydney, on 22 July 2028, will be the first there in over 150 years.
You know where the moon is at each phase. This lesson: when the sun, Earth and moon line up exactly.
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: every month?
ExploreTry it on the board and compare what happens with your prediction.
Explore: step through a year
Press Next full moon / Next new moon again and again. Watch the side view: where is the moon compared with the plane of Earth's orbit? Watch the top view: where is the orange crossing line when an eclipse happens?
Try it yourselfYour edits are saved in this browser.
Step through new and full moons until you have seen a solar eclipse and a lunar eclipse.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: conditions for an eclipse
In your book: draw a side view of the sun, Earth and moon for a lunar eclipse, and for a full moon without one. Shade the umbra and penumbra.
Solar eclipse or lunar eclipse?
Happens at new moon
Happens at full moon
The moon is between the sun and the Earth
The Earth is between the sun and the moon
The moon's shadow falls on part of Earth
The moon turns a dark redSunlight bent through Earth's air reaches the moon and is reddened, like a sunset.
Match each shadow to what you'd see from inside it.
Umbra
Penumbra
PractiseA few on your own, to check you have it.
Mix it up
Elaborate TypicalUse the same idea in a new context.
Elaborate: a flat orbit
Try it yourselfYour edits are saved in this browser.
Flatten the moon's orbit and step through at least four new and full moons.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: predicting eclipses
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
Solar eclipse: new moon, moon between sun and Earth, the moon's shadow falls on part of Earth.
Lunar eclipse: full moon, Earth between sun and moon, the moon passes through Earth's shadow (it often looks red).
Umbra: full shadow (total eclipse). Penumbra: partial shadow (partial eclipse).
The moon's orbit is tilted about 5°, so most new and full moons miss: eclipses come in eclipse seasons about every six months.
For teachers
Students state the conditions for solar and lunar eclipses, distinguish the umbra and penumbra, and explain why eclipses do not occur every month (AC9S7U03, node 3). About 22 minutes.
I can state the conditions for a solar and a lunar eclipse.
I can describe the umbra and penumbra.
I can explain why eclipses don't happen every month.
Before class
A concept tutorial for introducing or revising the idea; it pairs well with a lamp, a ball and a hoop tilted to show the moon's orbit. Set the width with ?width=minimum, typical (default) or wider.
The node isn't a hinge, but it depends on the moon-phase model (node 2): a student who thinks phases are Earth's shadow will confuse a lunar eclipse with a phase. The 3D step (the tilted orbit) is the hard part; the board shows it in a side view with the tilt and the shadows exaggerated.
Board notes: each step is half a month (29.5-day month). The line where the moon's orbit crosses the plane of Earth's orbit turns relative to the sun once every 346.6 days, so eclipse seasons come a little under six months apart; the board starts so that the first eclipses come in about month 4. Eclipse types use real angle limits (for example, a lunar eclipse is total when the moon is within about 0.4° of the plane). Solar eclipses are seen only from a narrow path or region of Earth. The 2028 total solar eclipse crosses Sydney on 22 July 2028.
Running the lesson
Engage: count how many chose 'every month'.
Explore: ask where the orange crossing line points when an eclipse happens.
Explain: the tilt question is the checkpoint.
The hard part (on purpose)
Thinking in three dimensions: the tilted orbit means the shadows usually miss. When a student expects an eclipse every month, ask what the side view shows at most new moons.
When students get stuck
A student says a lunar eclipse is the same as a new moon. Ask: Where is the moon in a lunar eclipse: between us and the sun, or behind the Earth? Fix: Behind the Earth, at full moon: Earth's shadow falls on it.
A student thinks the moon's shadow covers the whole Earth in a solar eclipse. Ask: How big is the umbra where it reaches the Earth? Fix: Small: the total eclipse is seen only from a narrow path.
Stretch and support
Stretch: Why do lunar eclipses happen at the same 'season' as solar eclipses, about two weeks before or after?
Support: Give side-view outlines of the sun, Earth and moon in a line, to shade the shadows.
Where it leads
Next: tides (node 5).
In class: a lamp, a ball and a tilted hoop; look up the next eclipses visible from your town.
What each step is for
Engage: every month?: Students who reason in 2D expect an eclipse at every new and full moon; the side view shows the tilt that prevents it.
Explore: step through a year: Stepping through a year of new and full moons and watching the side view shows eclipses only when the moon is near the plane of Earth's orbit.
Explain: conditions for an eclipse: Stating the conditions for each type, the two kinds of shadow and the tilt explanation are the node's three criteria.
Mix it up: An eclipse needs a particular line-up of the sun, Earth and moon, so the phase positions come back first.
Elaborate: a flat orbit: Removing the tilt in the model and getting an eclipse every time shows the tilt is the reason, not a detail.
Elaborate: predicting eclipses: Seeing why eclipses seemed unpredictable without a 3D model connects the physics to the history of science.
Now you can
State the conditions for a solar and a lunar eclipse.