Leaves change color in the fall due to a combination of factors, including leaf pigments, length of night, and weather. During the warmer months, leaves are green because of the chlorophyll they use to absorb energy from sunlight during photosynthesis. As the season changes, temperatures drop and days get shorter, and the chlorophyll in the leaves breaks down. The lack of chlorophyll reveals yellow and orange pigments that were already in the leaves but masked during the warmer months. Darker red leaves are the result of a chemical change: Sugars that can get trapped in the leaves produce new pigments (called anthocyanins) that weren’t part of the leaf in the growing season. The timing of color changes and the onset of falling leaves is primarily regulated by the calendar as nights become longer. The amount and brilliance of the colors that develop in any particular autumn season are related to weather conditions that occur before and during the time the chlorophyll in the leaves is dwindling. Temperature and moisture are the main influences. The amount of moisture in the soil also affects autumn colors. The best colors are produced when the weather is dry, sunny, and cool. The change in the length of day triggers several processes to get ready for the autumn and winter, and these changes can influence the shift in color to occur. Light energy is used to make anthocyanin, so sunny days can intensify the color development. Wind and rain are mechanical forces that can cause the leaves to detach and fall.