Today on Science Mysteries…Explained!, we’re going to ask that age-old science question that thousands of kids (and a few adults) are asking just about now: “Why do leaves change color in the fall?” Some trees and bushes have leaves that change color each autumn. In fact, in some regions of the world, forests look like someone took bright crayons and scribbled all over them in fall! Why does this happen? It’s all thanks to a special molecule called chlorophyll. Chlorophyll is a unique molecule called a pigment. A pigment is able to absorb certain wavelengths of sunlight. Chlorophyll absorbs all colors of light (white light is made up of all the different colors you see in a rainbow) except green. This means that it reflects green light. As a result, when we look at most plants, they appear green.

Chlorophyll’s main job is to help plants harness the energy in sunlight to make food. In the autumn, when there are fewer hours of sunlight, some trees, known as deciduous trees (deciduous means that their leaves fall in the autumn), begin to make less chlorophyll. As a result, their leaves no longer reflect green light as they did in the spring and summer. When this happens, leaves reveal some of the other pigments that were hidden before. These hidden pigments are different colors, such as yellow, orange, red, and purple. They can’t be seen in the spring and summer because the leaves on the trees are green thanks to chlorophyll. But when there is less chlorophyll in the fall, they really put on a show.