Sky Color Mystery

Learning Guide

A simple guide to lead you through the kickoff, the core challenge, and everything in between.

Mai’s Tips

1. Observation is key: The subtle blue tint from the side of the glass can be hard to spot at first. Ensure the room is dark enough and the background is truly dark. This step relies on noticing that faint blue, so guide their eyes carefully.
2. Milk concentration: Too much milk will make the water opaque and block too much light. Start with just 1-2 drops. If no effect, add one more drop at a time. The goal is a very dilute colloidal solution for optimal scattering.
3. Analogy fallback: If 'wavelength' and 'scattering' are too abstract, simplify. 'Wavelength' can be 'how jumpy a color of light is' (blue is very jumpy, red is less jumpy). 'Scattering' can be 'light bumping into tiny things and getting sent in all directions, like popcorn popping everywhere.'
4. Safety note: While this activity is generally safe, remind children not to drink the milky water. Small spills are possible, so have a cloth ready.

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1Breakfast Table Blue 3 min

• While having breakfast, encourage your child to look outside or at a picture of the sky. Discuss its color and ask them to share their initial thoughts on why it's blue, specifically asking why it isn't green. Listen to their ideas without correcting. Younger children can simply observe and name the color 'blue'. Older children can offer theories like 'clouds block other colors' or 'it's the ocean reflecting'.

Know Before You Teach

• Good to know: The sky's color is due to how sunlight interacts with Earth's atmosphere.
• Sunlight is 'white' but contains all colors of the rainbow.
• Children often have intuitive theories, like the sky being a reflection of the ocean.
• If they're stuck: Ask 'What color do you see most often when you look up during the day?' then 'Have you ever wondered why?'
• Easier: Focus only on 'What color is the sky?' and 'What do you think makes it that color?'
• Harder: Ask 'Does the sky always look the same color? What makes it change?'

Done when: Student has expressed an initial idea or wonder about the sky's color.

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2Explore & Plan Our Sky Experiment 7 min

• Gather all the materials together. As you do, assign roles or discuss what each item will represent. For example, the flashlight is the sun, the water is the air, and the milk represents tiny particles in the atmosphere. Ask for predictions before you begin the experiment itself. For younger children, ask simple predictions like 'Will the water change color?' For older children, ask 'What colors do you expect to see from different angles, and why?'

Know Before You Teach

• Good to know: This stage sets up a model for the Earth's atmosphere and the sun.
• Milk particles are larger than air molecules but small enough to demonstrate scattering.
• Predictions help engage critical thinking and provide a baseline for comparison.
• If they ask: Will the water turn blue? Let's make a prediction first! We'll find out when we do the experiment.
• It's working when: Child making a specific prediction, even if it's incorrect, demonstrating active thinking.
• If they're stuck: Suggest thinking about what happens when you shine a light through dusty air – can you see the light beam?

• Easier: Focus on gathering materials and asking simple 'what if' questions.
• Harder: Ask 'How is our model similar to the real sky? How is it different?'

Done when: Student has gathered materials and made a prediction about the experiment's outcome.

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3Unpacking Light and Scattering 7 min

• Explain these key terms in simple language. Have a clear definition ready for 'scattering' and 'wavelength.' Discuss what changed. Ask them:

  • 'What happens when light hits tiny things in the air?'
  • 'How are blue light waves different from red light waves?'
  • 'Which do you think scatters more: short, wiggly blue waves or long, stretched-out red waves?'

  Younger children can focus on the idea of light being 'bouncy' (scattering) and different 'colors' of light. Older children can grasp the concept of 'wavelength' and its relation to color and scattering. The goal is for them to grasp that different colors scatter differently.

Know Before You Teach

• Good to know: Scattering is the process where light waves are redirected by particles in the medium.
• If they ask: Why does green light not scatter the most? Green light does scatter, but blue light's waves are even shorter and wavier, making blue scatter more effectively than green.
• Key words: Wavelength: How squiggly or stretched out a light wave is. Different colors have different wavelengths.
• Key words: Scattering: When light bumps into tiny things and bounces off in all different directions, like a ball hitting a bumpy wall.
• It's working when: Child grasping the idea that some light colors 'wiggle' more than others and that light 'bounces' off things.

• If they're stuck: Use physical analogies: 'Imagine trying to run through a crowd with short, quick steps versus long, slow strides. Which would bump into more people?'
• Easier: Focus on the idea that light is made of colors and some colors 'bounce' more than others.
• Harder: Ask 'If blue light scatters the most, why do we sometimes see clouds that are white or grey?'

Done when: Student can describe scattering and wavelength simply and predict which colors scatter more.

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4Creating Our Mini Sky 10 min

• Set up the experiment carefully. Guide the child through each step, allowing them to perform actions like pouring water, adding milk, and holding the flashlight. Emphasize observation from two perspectives: looking from the side of the glass, and looking directly through the glass at the flashlight. Encourage descriptive language for the colors they see. Younger children can focus on seeing 'blue' from the side and 'yellow/orange' when looking directly at the light source. Older children can describe the process and relate it to the earlier discussion about scattering. Ensure they observe both the clear water and the milky water. This stage is done when they have clearly seen the different colors from different angles with the milky water.

Know Before You Teach

• Good to know: When light passes through a colloidal suspension (like milk in water), shorter wavelengths (blue) are scattered more in all directions, making the solution appear bluish from the side.
• The light that passes directly through will have lost most of its blue component, appearing more yellowish or reddish.
• This phenomenon is called Rayleigh scattering, which explains sky color and sunsets.
• It's working when: Child pointing out the blueish tint from the side and the yellowish/reddish tint when looking directly through.

• If they're stuck: Try adjusting the amount of milk (add a tiny bit more if too clear, or dilute if too cloudy). Ensure the room is dark.
• Easier: Focus on simply observing the colors and saying 'Look, blue here, yellow here!'
• Harder: Ask 'How does the direction you look change the color you see? What does that tell you about where the light is going?'

Done when: Student has observed the color changes in the milky water from different angles.

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5Connecting Our Sky to the Real Sky 3 min

• Facilitate a discussion that links their experiment observations to the real world. Ask them:

  • 'What color did the water look from the side, and why was that like the sky?'
  • 'What color did the flashlight look when you looked straight through the milky water, and when do we see that in the real sky?'
  • 'Why did we see blue, and not green, from the side?'

  Younger children can simply state 'the sky is blue because blue light bounces more.' Older children can explain scattering and relate blue's shorter wavelength to why it's the dominant color we see.

Know Before You Teach

• It's working when: Child connecting the colors they saw in the glass to the colors of the real sky and sunsets.
• If they're stuck: Re-point to the glass: 'Remember how it looked blue from the side? That's what the sky is doing!'
• Easier: Confirm: 'So the sky is blue because blue light bounces around a lot!'
• Harder: Ask 'If Earth had no atmosphere, what color would the sky be?'

Done when: Student can explain why the sky is blue using concepts from the experiment.

Your Notes