Module 2 of 13
Shadow Lab
Hold your hand up near a lamp. Look at its shadow on the wall. Now move your hand closer to the lamp. The shadow gets bigger! Move it away. Smaller and sharper. You just did the exact same physics the Moon does. Today, you are going to measure it — like a real scientist.
Light makes shadows.
Light travels in straight lines. If something blocks the light, you get a shadow — a dark shape where the light cannot reach. Your body blocks light. So does the Moon.
Bigger is not always darker.
Move a ball closer to a lamp and its shadow grows — but the edge gets fuzzy. Move it away and the shadow shrinks — but the edge gets sharp. There is a dark centre and a fuzzy edge.
The Moon's shadow on Earth.
The Moon is far away — about 400,000 km. Its shadow lands on Earth as a small dark spot, only about 240 km wide. That is smaller than many countries! Around the dark spot is a much bigger half-shadow, where people see a partial eclipse.
Umbra and penumbra.
Scientists give the two parts names. The dark centre is the umbra — say 'UM-bra.' The fuzzy edge is the penumbra — 'pen-UM-bra.' To see totality, you must stand inside the umbra. Our beach in Tarifa is inside it. Lucky us!
Why the shadow is small.
The Moon is much smaller than the Sun — 400 times smaller. But it is also about 400 times closer to us! That is an amazing coincidence. It means the Moon and the Sun look almost exactly the same size in our sky. That is why the Moon can cover the Sun so perfectly.
Measure the Shadow
This one is a team job — ask a grown-up to help! One person holds the torch still, one person holds the ball, and one person measures the shadow on the wall. If it is just the two of you, the grown-up can hold both the torch and the ball. Darken the room and put the torch about two metres from the wall, with the ball in the beam between them. Hold the ball 30 cm from the torch — about one ruler long — and measure how wide the shadow is on the wall. Then move the ball to 60 cm from the torch — two rulers — and measure again. Then move it to 100 cm from the torch — a whole metre! — and measure one last time. Type in your three numbers.
Wow Corner
The Moon's shadow races across the Earth at more than 1,700 kilometres per hour — about twice as fast as a passenger jet! At the very start and end of the path it goes even faster, like a race car on the curve of the Earth.
for grown-ups — long-press to open
Grown-ups Corner
Closer to the shadow's centre line = longer totality. Tarifa sits near the northern edge of the path, so we get 4m37s vs 6m23s at the centre. The 30/60/100 cm data shows a non-linear shrink — ask your child to guess why.