We've changed our name — alarm-clock.org is now timeandspace.science. Same tools, same pages, new address.

One machine, three clocks: the day, the month and the year

Grades 5–6 · 45 minutes · Measure it. The driving question: The day, the month and the year — how does one machine keep all three clocks? Every step below is a link that opens the exact view — one link puts the projector and every student screen on the same sky. Part of the lesson plans by topic and grade.

Before the lesson — what this assumes

Assumes: day and night come from the Earth's turn, and the moon goes around the Earth — names, not mechanisms; the mechanisms are today.
Pre-work (5 minutes): open the Sun, Earth and Moon simulator, find Play and the day / week / month span control, and drag the slider once. Nothing else.
For the teacher: the classroom guide covers projector setup, and the simulator's own scale card explains its exaggerations — the lesson leans on it in task 4.

The plan — every step carries its minutes

Warm-up · 5 minThree clocks run in the sky: one takes a day, one about a month, one a year. Ask the class to name what each clock measures before touching anything — most can name the day, few the month, and the year usually gets "the seasons?", which is exactly right.

Task 1 · 8 minThe day. Set the span to one day (the link opens on your own town) and Play. The sun arcs over; the read-out gives its altitude and direction live. Ask: what is actually moving — the sun, or us? Check the read-out's sunrise time against the town's sun page: same number, because both are computed from the same sky.

Task 2 · 8 minThe month's first clue. A week on the slider: now the moon visibly crawls along its orbit while the sun laps daily. Watch moonrise — later every day, by most of an hour. The moon's slowness against the sun's daily lap is the whole reason a "month" exists.

Task 3 · 8 minThe month itself. A month on the slider, Play: one full lap of the moon, and the phase disc beside the read-out runs new → quarter → full → back. Use the jump-to-next-phase control to land exactly on the next full moon, note its date, and verify it against the moon calendar.

Task 4 · 8 min"Is that picture true?" Scroll to the simulator's scale card and read it aloud: it states, in numbers, how much too close the moon is drawn and how much too close and too small the sun is — figures the page computes from its own drawing. Then the corridor version: at 16 mm to the Earth, the moon is a peppercorn 48 cm away and the sun a 1.7 m ball 188 m down the corridor. A drawing that confesses its lies, with numbers, is a scientific drawing.

Task 5 · 5 minYour own sky. The link-builder on the simulator page writes a URL for any place, date and span. Each pair builds the link for a date that matters to them — a birthday works — and reads off the moon's phase that night.

Wrap-up · 3 minThe board, in their words: the day is the Earth's turn; the month is the moon's lap; the year is the Earth's lap. One machine, three clocks — and next lesson's question is what happens because the three never divide evenly.

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

Day span: the sun's arc and the turn behind it; the read-out's sunrise matches the sun page's, because one sky is being computed.
Week span: moonrise slips ~50 minutes a night (the 5–6 moon lesson measures this properly).
Month span: the phase cycle completes in ~29.5 days; the jump-to-phase date matches the calendar.
The scale card's own numbers — read them off the card, they update with the drawing.
Different birthdays give different phases: the phase is a fact about the date, the same everywhere on Earth.

Standards: MS-ESS1-1 foundations (cyclic patterns from the Earth–sun–moon system), built on 5-ESS1-2.

What the picture fakes: The simulator's own scale card computes how wrong its picture is from the drawing's real geometry — the moon drawn tens of times too close, the sun thousands — so the disclaimer updates itself and can never go stale. Read the numbers off the card, not off this page.

Questions to chase on your own

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

Build a simulator link for the day you were born and find your birth moon. Compare with a friend's — same date, same phase, any town?
Using jump-to-next-phase: how many days from the next new moon to the next full moon? Is it always half of 29.5?
Watch all three bodies moving at once: the moon's grey patch always faces the Earth while its lit half always faces the sun. Explain, in one sentence, why that pair of facts IS the phase cycle.

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 isn't there a solar eclipse every day? The moon's right there next to the sun!
A kid watching this very simulator asked exactly this, and it deserves a real answer. The daily lap you're watching is us — the Earth's turn sweeps the sun and moon across the sky together, like two pictures on a spinning wall; the moon barely creeps along its own orbit in one day. Watch all three bodies moving at once and you can see it: the moon only actually passes the sun once a month (that's what a new moon is) — and even then it usually misses, because its orbit is tilted 5°, which at the sun's distance means passing ten sun-widths above or below. And on the rare month it does hit? The shadow's tip touching Earth is only ~100 miles wide. Any one town waits, on average, about 375 years for a total eclipse. That's why people cross oceans for four minutes of darkness.

Why does the moon follow me when we drive?
Because it is absurdly far away. Trees and houses slide past because a mile of driving changes your angle to them; a mile of driving changes your angle to the moon by nothing your eye can detect — it is a quarter of a million miles away. Only impossibly distant things "follow" you. The moon follows the car because of the exact distance the corridor-walk in task 4 is about.

If the Earth is spinning a thousand miles an hour, why can't I feel it?
For the same reason you can pour a drink on a smooth flight: you, the air, and everything around you are all moving together, and your body only feels changes in motion. The spin does show itself, though — it's why hurricanes rotate, and why the simulator's sun arcs across the sky at exactly 15° an hour. You can't feel the turn, but you can clock it.

Go further — beyond this site

NASA Space Place: Moon Phases — the month clock, drawn for this age.
NASA: Earth's Moon — the reference behind the month's numbers.

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 measure it rung.

All lesson plans

Teachers: make this lesson better

You are the one standing in front of the class, so you will see what we cannot: a task that runs long, a question that lands better another way, a grade level pitched wrong, a topic we should build next. Tell us — improvements go into the page, and if we use yours, your class gets the credit on it, the same promise the classroom request form makes.

💡 Question, problem or idea? Tell us →