Many of us in the Northern Hemisphere, Earth are enjoying autumn. For me, every year at this time the weather is comfortable, waves are up for surfing, beaches are empty, and for those of us more northern, the leaves of deciduous plants are changing colors, providing us vibrant purple, red, orange, yellow, and green nature scenes.
I enjoy observing the natural world and learning from the individuals who have studied it for millennia. Do you know why leaves change colors? The Earth, it seems, has been revolving for more than 4 billion years around the Sun, as the Sun itself travels through the Universe.
When the Earth reaches this part of its annual path, the northern hemisphere is tilted away from the Sun’s light and heat. Because of the shortening of the length of daylight and cooling temperatures, leaves are signaled chemically to stop their food production. When chlorophyll, the extraordinary green chemical that absorbs from sunlight the energy that is used in converting carbon dioxide and water into so much of the world’s food, sugars, and starch, breaks down, the yellow to orange pigments of carotenes and xanthophyll are unmasked. Other chemical reactions develop red anthocyanin.
