The next time you get the opportunity to blow some soap bubbles, be sure to take a long, close look at them. Those ever-changing rainbows sliding around across the surfaces of the bubbles can be spellbinding… like an atmosphere on a bubble planet. But why do we see them? It’s a water and soap molecule sandwich! From the Exploratorium:

The colors of a soap bubble come from white light, which contains all the colors of the rainbow. When white light reflects from a soap film, some of the colors get brighter, and others disappear…

A bubble film is a sort of sandwich: a layer of soap molecules, a filling of water molecules, and then another layer of soap molecules. When light waves reflecting from one layer of soap molecules meet up with light waves reflecting from the second layer of soap molecules, the two sets of waves interfere. Some waves add together, making certain frequencies or colors of light brighter. Other waves cancel each other, removing a frequency or color from the mixture. The colors that you see are what’s left after the light waves interfere. They’re called interference colors.

As the bubble walls thin, the colors change, before pop! Try the Bubbularium experiment at Exploratorium.edu.

Next: The Bubbleologist makes efficient shapes with bubbles and The Bubble Artist. Plus, more bubbles and more iridescence.

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