How do you explain iridescence to a 5 year old?

Some things reflect light in different colors depending on how you look at them. Like hologram picture cards, as you move the card, it looks like the picture is 3D or is moving. On things like bugs or soap bubbles, the different surfaces are so tiny that you see them all at the same time without having to move around. This is what makes them look rainbow-colored.

The best way to explain a child what iridescence is all about is direct observation. Make sure you have some soap bubbles or a compact disc. Show your child how the surface of these objects changes color as the bubbles move around or when you move the cd and change the angle of view. You might want to try to spot some iridescent clouds in the sky even though the phenomenon is not that common. You can use a pearl necklace instead.

You could also do some experiments with water mixed with soap in a bowl. Show your child what happens when you move the bowl from one angle of illumination to another. Some bugs, birds and some butterflies also show beautiful effects of phase shifts and hue changes.

Tell your kid that all the colors of the rainbow are somehow hidden inside every object. Some objects only show one color, like the leaf of a tree which is green in spring. Some other objects can show all the colors they hide when the light hits them.