A newsletter for unflinching, ever-curious science-lovers. ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏
October 10, 2025—The science of changing leaves, RFK, Jr., cites "appalling" studies in his latest claims, and two earthquake fault lines may be operating in sync. —Andrea Gawrylewski, Chief Newsletter Editor | | DenisTangneyJr/Getty Images | | - Where will the best leaf peeping be this year? Expert predictions and more below. | 6 min read
- At just the right moment both planet Earth and the moon could be visible from the surface of Mars. This is how. | 5 min read
- Yesterday in a cabinet meeting, U.S. secretary of health and human services Robert F. Kennedy, Jr., claimed that there is a link between autism and circumcision, citing what experts call "appalling" studies. | 3 min read
- Two geologic faults, the San Andreas and the Cascadia Subduction Zone, have produced several synchronized earthquakes in the last 3,000 years. | 4 min read
- Babies are born with high levels of Alzheimer's-associated proteins in their brains. This could help researchers devise new treatments for the disease. | 5 min read
- What's it like to be the president's doctor? We sit down with a former White House physician who reveals the medical realities of caring for the president of the U.S. | 20 min listen
| | If you live in the Northern hemisphere, you might be witnessing a brilliant transformation: the metamorphosis of tree leaves. Across history, people around the world devised legends to explain the vivid fall foliage. Today, we dive into how science explains why green leaves develop fiery, warm tones, and why they eventually fall. Leaf color: Changes in leaf color are catalyzed by diminishing daylight in the fall. When daylight hours shorten, veins that bring water and nutrients to the leaves gradually close off. Without these nutrients, chlorophyll—the green pigment found in leaves—disappears. Yellow and orange pigments, which were always there but hidden, become visible. Meanwhile, red pigments form as sugars in the leaf react with chemicals. Color intensity: The intensity of the colors, on the other hand, changes when the air temperature lowers. Bright days and cold nights trap more sugars in the leaf and cause red colors to brighten. And dry weather triggers the production of a hormone called abscisic acid that signals to the tree to drop its leaves. This dramatic drop reserves the trees' limited supply of water for its roots during the arid winter. Tree health: Fall leaf color is a sign of tree health. Foliage that turns bright yellow, orange, red or purple as days shorten means that a tree is on schedule to shed its leaves in preparation for winter. But if the timing or color progression is off, this could signal that a tree is struggling. A summer drought can cause a tree to shed its leaves early. Meanwhile, wet and rainy fall seasons can promote the growth of fungi and pests, which can soak up a tree's resources and dampen the vibrancy of its foliage. Climate change: As temperatures warm, some researchers expect less vibrant autumn seasons. Milder autumns mean that trees with different coolness thresholds for color changes will begin their winter preparations at different times, spread over more weeks, rather than changing around the same time. And warmer temperatures extend the leaf dying phase–called senescence—meaning that once leaves lose their green color in autumn, they begin producing CO2, which further contributes to global warming. Viewing tips: Check out this map researchers created to predict where the leaves will be at their best this year. According to a forecast from AccuWeather, the best fall foliage is expected in New England, the Colorado Rockies, the Plains and the Midwest, whereas regions such as the Appalachians and Pacific Northwest may see duller color or early leaf drop. — Andrea Tamayo, Newsletter Writer | | | | |
- Test your science chops by taking today's quiz! Also, try to solve Spellements and our killer version of Sudoku. This week, Joaquin M. found the word affine in the Spellements puzzle. It's an adjective used in mathematics that means preserving the relationship between lines (like their parallel-ness). Impressive!
| | MOST POPULAR STORIES OF THE WEEK | | -
Prime Numbers Show Unexpected Patterns of Fractal Chaos | 5 min read - Math's Most Tangled Mysteries Start With a String | 5 min read
- See Stunning Feline Photography Revealing the Science of Cats | 4 min read
| | Fallen leaves serve as a vital shelter for pollinator insects and helps them survive the winter. Fallen sticks and branches and dead garden plants are nesting sites for butterflies, bees, moths, and even fireflies until spring. This fall, if you can resist cleaning leaves off your lawns and cutting down dead gardens, the natural world will thank you. Regular readers of this newsletter also know that I often get bold and support eliminating lawns entirely! | | Wishing you a restful weekend (especially now without leaf gathering duty). You can always email me: newsletters@sciam.com. See you Monday. —Andrea Gawrylewski, Chief Newsletter Editor
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