Visualizing and Understanding Lunar Eclipses

Using simple items, the children simulate the Sun-Earth-Moon system to understand how a lunar eclipse works. They also develop an appreciation for the achievements of ancient Greek philosophers who were successful in deriving the correct explanation for this phenomenon. This simulation reinforces the children’s skill of attaining different perspectives of observation.

After carrying out this activity, the children will be able to:

• explain how lunar eclipses work.
• name the ancient Greek philosopher who found the correct explanation for this astronomical phenomenon.

Invite the children to help Anaxagoras to recreate a lunar eclipse using their models. Ask them the following questions:

1. Where should we place the Moon when using the models?
2. When viewed from Earth, which lunar phase does this correspond to?
3. Which shape has the shadow of the Earth?
4. What could Anaxagoras conclude from the shape of the shadow? Which shape does the Earth have?

• A flashlight or lamp
• A UNAWE Earthball or globe
• A model of the Moon, for example a Styrofoam ball
• A paper figure of Anaxagoras, to be placed on the Earthball
• A sheet of white paper

Since the dawn of history people all around the world became very scared each time the sunlight vanished during daytime. Most of them thought that this was a divine punishment. In 500 BCE, and 100 years after Thales, the Greek natural philosopher called Anaxagoras, born in the city of Clazomenae (today’s Turkey), searched for explanations for astronomical phenomena. He succeeded in finding the causes of lunar eclipses and was the first to bring natural philosophy to Athens. During a lunar eclipse, the Sun, Earth and the Moon are aligned in a straight line. The Earth blocks any direct sunlight from reaching the full moon. The Moon is then covered by the Earth's shadow. During a lunar eclipse the Moon turns reddish, because the sunlight travels through the Earth atmosphere. The same phenomenon also causes the red sunsets.

Switch on the flashlight or lamp and place the Earthball/globe in front of it. Take the sheet of paper and place it behind the Earth like shown in figure 9. Do you see the Earth shadow projected on the sheet of paper? Observe the shape. Can you describe it?

Fig. 9 The Earth globe projects a shadow on the sheet of paper (Credits: Scorza)

Now take away the sheet of paper and move the model of the Moon such that it enters the shadow of the Earth. If you look carefully you will notice that the Moon’s surface will lose brightness as it travels behind the Earth and enters the Earth’s shadow. This is a lunar eclipse! It happens when the shadow of the Earth covers the Moon. It lasts for about one hour, because the Moon needs time to travel through the shadow of the Earth.

Fig. 10 The Earth projects a shadow on the Moon (Credits: Scorza)

Space Awareness curricula topics (EU and South Africa)

The journey of ideas, Solar system