File:Fall in the Appalachian Mountains (MODIS 2021-11-15).jpg

English: As temperatures dropped and sunshine shortened across the Appalachian Mountains in early November 2021, the forests burst into breathtaking autumn color. The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired this true-color image on November 8.

The ridges and valleys of the Appalachians seen in this image curve from eastern West Virginia (top right) to Georgia (lower left). Most of the valleys appear bright green, but the deciduous forests at higher elevations wear a blanket of orange and red. To the west and in the coastal region east of the Appalachian, broad swaths of gold and golden-green mark the colors of spent agricultural crops and add to the beauty of a sunny autumn day.

The magic that spurs the glorious colors of autumn is driven by chemistry. Green leaves are rich in chlorophyll, a molecule that plants use to synthesize food. Chlorophyll absorbs the red and blue portions of sunlight, and so the reflected light—which gives the leaf ifs color—looks green. Chlorophyll isn’t a very stable compound, so plants have to continuously make it to keep their leaves green, and they do this when there is plenty of sunlight and warm temperatures. When temperatures drop and days shorten, levels of chlorophyll drop as well.

Leaves contain other pigments, depending on the type of tree, such as carotenoids and anthocyanins. As chlorophyll fades, the other colors become visible. Carotenoids show up as yellow and anthocyanins appear red. Each species of tree contains different amounts of pigments, which makes it possible to generalize what color a given type of tree in the fall. According to the U.S. Forest Service, Oaks generally turn red, brown, or russet; aspen and yellow-poplar turn golden. Maples differ by species. Red maple turns brilliant scarlet; sugar maple, orange-red; and black maple, yellow. Leaves of some trees, such as elms, simply become brown.

To visualize the dramatic change that occurred between September 24, and November 8, the NASA Worldview App allows a comparison of this region on those two days. To view the comparison, click here.