Why is the Sky Blue?

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In this activity, learners use a flashlight, a glass of water, and some milk to examine why the sky is blue and sunsets are red. Learners will discover that the sky appears a different color depending on the position of the sun as well as molecules and particles in the air that cause the scattering of light. [Activity is publicly available through a web crawler capture on Archive.org.]

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
1 cent - $1 per group of students

Age Range:
Ages 11 - 18

Resource Types:
Activity, Experiment/Lab Activity, Simulation


Materials List (per group of students)

  • a large glass jar or vase
  • water
  • milk or powdered milk
  • a flashlight
  • a dark room


  • Earth and Space Science
    • Earth Structure
      • Atmosphere
    • Earth, Moon and Sun
    • Solar System
      • The Sun
  • Physical Sciences
    • Vibration and Waves
    • Light and Optics
      • Sunlight and Color
    • States of Matter
      • Gases
    • Structure and Properties of Matter
      • Elementary Particles and Nuclear Physics
  • The Nature of Science
    • The Scientific Process
      • Conducting Investigations

Informal Categories

  • Food and Cooking
  • Nature and Environment


To use this activity, learners need to:

  • see
  • see color
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


Access Rights:

  • Free access