Mystery Image Contest: April 1-15, 2014


Look at the orange circles in the image above—the one on the left looks smaller than the one on the right, doesn't it? Actually, the orange circles are geometrically the same size! It's your brain that gets fooled into thinking that they are different sizes because of the blue circles that surround them. The image above is a famous example of an optical illusion, called the Ebbinghaus illusion. Optical illusions like these lie at the intersection of mathematics and psychology. Though it's tempting to think that your brain always correctly interprets the world around you through your eyes, this isn't always the case. Illusions like the Ebbinghaus are able to take advantage of certain quirks in the way your brain works so that things that are demonstrably true mathematically (e.g., that the two orange circles are the same size) truly appear differently to you. Scientists believe that the Ebbinghaus illusion fools your brain using the space between each orange circle and its surrounding blue circles: the larger the distance between an orange circle and the surrounding blue circles, the smaller the orange circle appears to be. So even though the orange circles are geometrically identical, they look different in size based on the objects around them.


This image is of the Ebbinghaus illusion.

Photo Credit

Public domain

For Educators

Teaching Support

This Mystery Image Contest coincides with the theme of the April 2014 Mathematics Awareness Month: Mathematics, Magic, and Mystery. The theme focuses on problems and phenomena in mathematics that go beyond the realm of the logical or the intuitive and require creative thinking and a sense of wonder to comprehend them. Optical illusions such as the Ebbinghaus illusion could be considered one of these phenomena.

In addition to the related resources from Science NetLinks in the list below, the Mathematics Awareness Month website will be updated every day in April to introduce a new mathematical phenomenon. These phenomena will be accompanied by introductory videos and supplementary materials, perfect for educators who wish to incorporate these activities into their classroom teaching. Be sure to check out their theme description and their Mathematics Awareness Month poster as well.

Related Resources

What's in a Shape?
3-5 | LESSON
The Fibonacci Sequence
6-8 | LESSON
Seeing Eye to Eye with the Umpire
6-8 | LESSON
Mona Lisa’s Smile
Musical Illusion
Visual Math
Changing Illusions
3-8 | TOOL

Science NetLinks Mystery Image Contest Rules and Regulations

What Is the

Mystery Image Contest?

The Mystery Image Contest offers the chance to identify a science-related object based on a close-up picture of it.