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Have YOU EVER gotten a blood test result saying your vitamin D levels are low? Or heard that the vitamin is a miracle cure? It turns out fears about deficiencies, and hopes of the vitamin’s healing power, have been wildly overblown. Author Christie Aschwanden on page 28 explains why the evidence has pointed one way and then the other, and why blood tests can be misleading, in a story full of insights about the advancement of science. You need some vitamin D, though probably not supplements. We make vitamin D when sunlight hits our skin, like a human form of photosynthesis. The best way to get it, if you are able, is to spend more time outdoors—which tends to make everything better. Prepare to look at the night sky in a different way after reading Michael D. Lemonick’s article on page 20. The universe is full of . . . voids. They are empty spaces where almost nothing currently knowable exists. Mike is a former editor at Scientific American and a longtime physics writer (and the nicest guy), and he’s been following the mystery of the cosmic voids for decades. When they were discovered, they blew astronomers’ minds, but now we have enough data and computing power to study these empty spaces, which could improve our understanding of gravity, dark matter and dark energy. Depression can be a debilitating, chronic, episodic condition, and preventing it could save money, health and lives. Now there’s strong evidence that prevention programs can help. Screening teenagers and helping at-risk kids learn emotional and cognitive skills can reduce the risk of early signs turning into mental illness. Science writer Elizabeth Svoboda discusses on page 50 how to build these skills and why a focus on fixing rather than preventing problems makes it difficult for school systems to implement such programs. We hope our article will help broaden support for these kinds of initiatives. Prevention rarely gets as much appreciation as it deserves. The photographs of Alaska’s rusting rivers, beginning on page 36, are real—the rivers really do look brilliant orange, and that is literally rust. Climate journalist Alec Luhn accompanied scientists studying these bizarre rivers to figure out what is causing the discoloration, and photographer Taylor Roades used drones to capture the scenes. Alaska is warming even faster than the Lower 48, and thawing permafrost there is changing ecosystems dramatically. Acid from newly exposed bedrock could be leaching out iron that later forms rust, or it might be bacteria or some other force. Until recently, a general lack of feeling sexually attracted to others was often considered a psychological problem in itself or a symptom of some other disorder. Now asexual people and researchers who study asexuality have shown that it is just another way to be human. Allison Parshall, a writer and editor who works with us frequently (she edited this issue’s Advances department), has a thoughtful story on page 68 about the new cultural and scientific awareness of asexuality and how it is opening up new social norms. You may have read about the discovery of a long-sought mathematical shape called an einstein tile that can cover an infinite surface without repeating a pattern. I thought I’d heard all about it … but then I read computer scientist Craig S. Kaplan’s account of its discovery on page 58. It is a delightful narrative, full of dramatic tension and charismatic characters who are having an absolute blast pursuing a new understanding of tiling patterns. The illustrations by Miriam Martincic are inspired by M. C. Escher, the artist whose dazzling repeated patterns were popularized in the U.S. by Scientific American. Enjoy the challenge of mentally fitting these pieces together in your own mind.