Scattering of Light with Milk

A flashlight shining through water mixed with milk demonstrates how scattering of shorter wavelengths makes light appear blue from the side and red-orange when viewed through the length of the liquid, simulating why the sky is blue and sunsets are red.

1. Fill a clear glass pitcher or tall jar with water.
2. Add small amounts of milk until the water appears murky but still translucent.
3. Place a flashlight at the bottom or side so its beam shines through the mixture.
4. Observe the light from the side of the pitcher (90° to the beam); it should appear bluish.
5. Observe the light from the far end of the pitcher (180° to the beam); it should appear red-orange.
6. For better visibility, project the light onto a white index card and perform the experiment in a dark room.

Refraction of light during the transition from air to water made visible with milk - physikdigital • de:

Scattering of Light Using Milk - Science Made Easy:

📄 Sunset in a glass - Causes of Color: https://www.webexhibits.org/causesofcolor/14F.html

• Use a long, narrow aquarium to make the effect more dramatic.
• Compare results using whole milk, 2% milk, skim milk, or milk powder.
• Try adjusting the concentration of milk to change how much scattering occurs.

• Perform the experiment on a stable surface to avoid spills.
• Avoid getting water or milk on the flashlight or electrical components.
• Clean up spills promptly to prevent slipping hazards.

• Why does the sky look blue during the day but red at sunset? (Blue light is scattered in all directions by air molecules; at sunset, light travels farther through the atmosphere, scattering away most of the blue and leaving red-orange light.)
• Why does violet light not dominate the sky even though it has a shorter wavelength than blue? (The sun emits less violet light than blue, and our eyes are less sensitive to violet wavelengths.)
• How does the milk in the experiment represent Earth’s atmosphere? (The fat and protein molecules in milk scatter light, similar to how gases and dust scatter sunlight.)