Did you know that the Moon does not change size? Nor does it’s orbit change enough to make the moon look bigger or smaller to people on Earth. So why does the moon sometimes look bigger or smaller in the night sky? It’s all an optical illusion!

A common misconception about the Moon is its distance from the Earth. The Moon appears to be larger at times, so some people think that the Moon moves substantially closer to the Earth. While it is true that the Moon’s orbit around Earth is not exactly circular, the difference in distance from the Earth is so small that it does not affect how large the Moon appears in the sky. Many people think the phenomenon of the Moon appearing larger at times may be due, perhaps, to some sort of magnification caused by the Earth’s atmosphere.  However, this is strictly an optical illusion ~ the eye is tricked into measuring the Moon against nearby objects such as buildings, trees, and hills.  These types of objects, located on most horizons, create the illusion of increased size.  (The scientific term for this is oculomotor macropsia.)  This optical illusion is known more commonly as the Moon Illusion.

 First, gather your materials:
– A variety of round cookies/candies (M&Ms, mini Oreos, Lifesavers, Chips Ahoy cookies, Mother’s oatmeal cookies, etc.)

Procedure:

How big do you think the Moon is in proportion to the Earth?  If you look at the Moon when it’s full, how big does it look? Which of these cookies and candies can be compared to the size of the Moon in the sky when held at arm’s length?

Use the same cookies and candies and try to determine the approximate comparison of the size of the Earth and Moon.  Have them select the two items that they think represent the relative sizes.

Once your scientists have made their guesses, tell them that Earth’s moon diameter is about one-fourth the size of the Earth’s diameter.  Therefore the correct selection is the M&M (Moon) and the Chips Ahoy cookie (Earth).

Next have them place these two items so that they are at a scale distance from one another. The correct distance is approximately 156 cm from each other (the Moon is approximately 30 Earth diameters distance from the Earth). Have them use a ruler to see if they are correct in their approximation by measuring their items and the distance between them.  [Note: the M&M diameter will be about 1.3 cm; the Chips Ahoy diameter will be about 5.2 cm; and the distance between them will be 5.2 cm X 30 = 156.0 cm…. or 62.4 inches]

After making your guess for which of the treats (when held at arm’s length) is the same apparent size as the Moon, explain that the Moon will fit inside of the hole of the Lifesaver….always! Then, on the next full moon take your Lifesaver candy and head outside and see how perfectly the moon fits inside of the Lifesaver.