The Moon does not make its own light. Sunlight always lights up one half of it. As the Moon moves around the Earth, we see different amounts of that lit half. This is called a phase. One full cycle takes about 29 days.
Why does the Moon change shape?
Drag the Moon around its orbit. The left panel is the view from far above the Earth's North Pole — a view nobody has ever had. The right panel is what you would see standing in your own street that night.
Looking down from above
Sunlight comes from the left. Drag the Moon, or use the slider below.
Not to scale. The real Moon is about 30 Earth-widths away.
What you see from Earth
The same Moon, same moment, seen from the ground.
New Moon
Amavasya · Day 1
Day of cycle0.0
Lit part we can see0%
Paksha—
Tithi1
Try these three, one at a time
- Put the Moon directly opposite the Sun. How much of it can you see lit? Now put it between the Sun and Earth.
- Watch only the Moon in the left panel as you drag. Is half of it lit at every single moment — even when the right panel shows nothing?
- Press Play and count how many days pass before the shape repeats.
Two things this picture gets wrong
It is flat. The real Moon's orbit is tilted about 5°, so most months it passes above or below the Earth's shadow entirely. That is why we get phases every month but an eclipse only rarely — tick the shadow box to see the side view.
It is not to scale. The Sun is far bigger and much further away than anything drawn here.
TEACHER'S PLAN
The 40-minute period
Real object first, simulation second, explanation third. A child who only ever sees the screen learns the animation, not the science.
GRADE6 · CBSE / NCERT Curiosity Ch. 12
DURATIONOne period, 40 minutes
YOU NEEDA bare lamp or strong torch · one small ball per pair · curtains drawn
OUTCOMEThe student can explain that a phase depends on how much of the Moon's lit half faces Earth — and why this is not the Earth's shadow
5 minHOOK
Ask before you tell
Put one line on the board and nothing else: आज चाँद कैसा दिखेगा? — what shape will the Moon be tonight?
Ask who has waited for the Moon on Karva Chauth, or for the Eid moon. Who knows what Purnima and Amavasya mean? Most of the class knows these words without knowing the cause. Write three of their explanations on the board, including the wrong ones, unlabelled. You return to these at the end.
"The Moon doesn't grow and shrink. It's a rock, always the same size. So what is actually changing?"
5 minPREDICT
In the notebook, before anything else
- Draw the Sun, the Earth and the Moon at Amavasya. Mark where each one sits.
- In one sentence: why is the Moon dark that night?
Correct nothing yet. Walk the rows and count how many have drawn the Earth sitting between the Sun and Moon — usually more than half the class. That is the misconception this whole lesson exists to fix, and being wrong on paper is what makes them care about the answer.
10 minDEMO
The lamp and the ball
This comes before the screen. Lamp in the centre, everyone standing in a wide circle facing it. Each student holds a ball out at arm's length, slightly above eye level.
Their own head is the Earth. The ball is the Moon. The lamp is the Sun. Now turn slowly, all the way round, watching only the ball. Twelve seconds of turning reproduces one month — full when facing away from the lamp, dark when the ball is between them and it.
"Is half of your ball always lit? Even when you can see no light on it at all?"
Then ask the question the demo cannot answer: what would this look like from above the room? Nobody can get above their own head. That is what the simulation is for.
10 minSIMULATE
Use the simulator above
One rule, and it is the central science skill of this grade: change one thing at a time. Cover the left panel for the first minute and have them predict what the right panel will show — the prediction is what makes them look properly.
- Put the Moon directly opposite the Sun — the whole lit face points at Earth.
- Put it between Sun and Earth — the lit face points away from us.
- Press Play and count the days before the shape repeats.
Use the four jump buttons to move straight to a phase mid-explanation rather than hunting on the slider.
6 minEXPLAIN
Back to the three answers on the board
Ask the class which of their opening explanations survived. Then handle the three below head-on, because they will come up.
"The Earth's shadow falls on the Moon."
If that were true we would get an eclipse every single month. We don't. Tick the shadow box in the simulator: the orbit is tilted about 5°, so the Moon usually passes above or below the shadow. Phases happen monthly, eclipses don't — that difference is the proof.
"The dark part has no sunlight on it."
Point back to the ball. Half of it was lit at every single moment. There is no permanently dark side of the Moon.
"The Moon only comes out at night."
Ask them to look for it tomorrow afternoon. A waxing moon is easily visible in daylight. This one delights them.
NOTEBOOK ENTRY — DICTATE THIS
4 minTRANSFER
A question about the sky, not the screen
Draw a waxing crescent on the board, horns pointing left. "Tonight the Moon looks like this. Is it growing or shrinking? What will it look like in a week?"
Homework — the Moon diary
Ten nights. Each night: the date, the time, and a small drawing of the Moon's shape. Missed nights go down as "cloudy" — that is real data, not a failure.
Bring the diaries back and line them up on the wall. Thirty students' drawings from the same ten nights agreeing with each other is more convincing to an eleven-year-old than anything you or the simulator can say.
What to assess
Grade the reasoning, not the drawing. Three things tell you it landed:
- Does the student place the Moon between Sun and Earth for new moon — not the Earth in the middle?
- Can they say that half the Moon is always lit?
- Can they give one reason phases are not eclipses?
For fast finishers: "Design a test on the simulator that would prove to your friend that the Earth's shadow is not the cause."