Two months — and who decides what a supermoon is?

Before the lesson — what this assumes

• Assumes: phases as geometry (angle from the sun), fluently.
• Assumes: algebra with reciprocals — the lesson lives on 1/(1/a − 1/b).
• Pre-work: from the calendar, count the days between two consecutive full moons. Bring the number; it will disagree with the textbook's 27.3, on purpose.

The plan — every step carries its minutes

The minutes are there for the teacher's pacing — and so that any single step can be handed to a student as their own five-minute lesson. See students teach the class.

What they should find — the teacher's key

• 1/(1/27.32 − 1/365.25) = 29.53 d.
• The threshold-sensitivity exercise typically moves the year's count by 1–3 events either way.
• The site's stated-threshold policy is the model answer to the closing question.

Standards: HS-ESS1-4 practice; nature-of-science: definitions are choices.

What the picture fakes: The phase, illumination and rise/set times are solved from the real orbit for the class's own town. The simulator's view deliberately draws no Earth shadow — a drawn shadow would imply an eclipse every month, which is exactly the misconception the 7–8 lesson takes apart.

Questions to chase on your own

For the student who wants more — each answerable with the tools, no teacher required:

• If the moon's orbit lay exactly in Earth's orbital plane, how many lunar eclipses would there be per year? Defend the number.
• The blue moon page tabulates one definition and only explains the other. Read why — is that the right editorial call? Argue either way in three sentences.

Questions the curious actually ask

Real questions, mostly from real kids — the kind that sound simple and open trapdoors. Worth raising in class before someone raises them for you:

Why can I see the moon in the daytime?
Because the moon doesn't know about our night. It's above the horizon about twelve hours out of every twenty-four, and those hours drift through the whole clock as the month goes by — so roughly half of all moon-watching time is daytime. (Your town's moon page shows exactly when it's up today.) It's simply bright enough to beat the blue sky. The surprise isn't that you sometimes see a daytime moon; it's that anyone ever told you the moon belongs to the night.

Why does the moon look huge when it's rising?
Photograph it and check: the rising moon is exactly the same size in the picture as the high moon — your camera isn't fooled, but your brain is. This is the "moon illusion," and here is the genuinely great part: it has been argued about since the ancient Greeks and there is still no fully agreed explanation. It is one of the oldest open questions about your own mind, and you can run the experiment tonight with a phone.

Why does the moon turn red in an eclipse?
Because during a lunar eclipse the only light reaching the moon has skimmed through the ring of Earth's atmosphere — the same air that makes sunsets red. Stand on the moon during totality and you'd see why: the Earth, black, ringed by a thin band of fire that is every sunrise and every sunset on Earth happening at once. That's the light painting the moon. A blood moon is our own sky, reflected back at us.

Go further — beyond this site

• NASA: The Moon — reference figures for both months and the orbit's shape.
• NASA: Phases, Eclipses & Supermoons — NASA's own careful wording — compare it with the tabloids'.

Same question, other grades

Each grade band re-asks this topic's question one level deeper — observe it, describe the pattern, measure it, explain the mechanism, quantify it and question the model. This page is the quantify it — and question the model rung.