Astronomy Physics
Optics propagation of light
Age Group
16 17 18
Expected time
2 periods
Red moon.PDF
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Red Moon

What’s the mystery? When the Moon travels through the Earth’s shadow sunlight is blocked. However, instead of turning completely dark, the Moon gets a reddish colour. How is this possible?
Domain(s) Physics, astronomy.
Subdomain keywords Optics, propagation of light.
Age group 16 to 18 years old.
Expected time for the mystery Two 45-min lessons.
Safety/Supervision No need for safety measures.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials General:

  • Internet (for YouTube)

Experiment 1. Dispersion and refraction:

  • (White) flashlight (not LED)
  • Prism
  • (Glass of water, straw)

Experiment 2. Scattering of light:

  • (White) flashlight (not LED)
  • Large transparent container of water (~10 litres)
  • ¼ cup of whole milk (not skimmed)
Learning objectives
  • Learn about the light scattering properties of the atmosphere.
  • Learn about the refracting properties of the atmosphere and other mediums.
  • Learn why the sky is blue.
  • Learn why the sky turns red during a sunset.
  • Learn why the Moon turns red during a lunar eclipse.
Resources The teacher can watch the following YouTube video for more information on why the Moon turns red during a lunar eclipse:

Aa short video in which NASA planetary scientist Dr Shawn Domagal-Goldman explains why the Moon turns red during a lunar eclipse.