(Left to right): Museum of Southeast Denmark; Heli Maijanen; Oxford Science Archive Heritage Images/Newscom

Top stories: Disappearing Zika, tricky eclipses, and the world’s oldest ice cores

Three times scientists learned something from solar eclipses—and three times they were tricked

Next Monday’s solar eclipse has inspired millions to travel to the path of totality, where the alignment of moon and sun will cast the land into darkness for up to 2 minutes and 40 seconds. For most scientists, though, the celestial phenomenon won’t be such a big deal. Astronomers routinely study the sun’s wispy atmosphere using coronagraphs, telescope attachments that obscure the surface glare of the sun. But long before such high-tech instruments were available, eclipses helped lead to some key scientific discoveries.

Thousand-year-old Viking fortress reveals a technologically advanced society

When archaeologists uncovered four ancient ring-shaped fortresses in Denmark in the 1930s, the find profoundly changed the way they thought about the Vikings that built them. Rather than mindless marauders, Vikings in the Middle Ages must have been a complex, technologically advanced people to build these fortifications. Now, Danish archaeologists have described a fifth ring fortress—the first such discovery in more than 60 years—revealing even more about these architecturally gifted warriors.

Record-shattering 2.7-million-year-old ice core reveals start of the ice ages

Scientists announced this week that a core drilled in Antarctica has yielded 2.7-million-year-old ice, an astonishing find 1.7 million years older than the previous record-holder. Bubbles inside contain greenhouse gases from Earth’s atmosphere—including carbon dioxide—from a time when the planet’s cycles of glacial advance and retreat were just beginning, potentially offering clues to what triggered the ice ages. Atmospheric carbon dioxide levels in the core do not exceed 300 parts per million, well below today’s levels.

Knee arthritis in Americans has doubled since 1940

Knees hurting? You wouldn’t be alone. The prevalence of knee arthritis among people in the United States has doubled since the start of World War II, according to an unusual study of more than 2500 skeletons, including some dating as far back as 6000 years. Even after researchers corrected for the recent growth in U.S. waistlines and life spans, the increase still held, meaning—say scientists—that other, still unknown, factors are causing more people to suffer from aching knees.

Zika has all but disappeared in the Americas. Why?

One. That is the total number of locally transmitted Zika cases confirmed in the continental United States this year, as of mid-August, contrasting with hundreds of cases of local transmission last year. Better control of Zika's vector, the Aedes aegypti mosquito that thrives in the hotter, southern part of the country, doesn't explain the dearth of cases. Nor are other factors such as climate change at work, experts say. Instead, Zika cases have plummeted in Latin America and the Caribbean, where the virus raged over the past 2 years, and much of the population is now immune to it.

An MIT professor’s bittersweet departure for astronaut training

There was a time when aerospace engineer Warren “Woody” Hoburg wouldn’t have thought twice about swapping his tenure-track faculty position at the Massachusetts Institute of Technology in Cambridge (MIT) for the chance to become an astronaut. But when NASA called in early June to say he had beaten the 1500-to-one odds of being chosen for its next astronaut class, the deeply-engaged professor was conflicted. But ultimately he couldn’t resist NASA’s offer, and resigned from MIT, which made him a verbal promise that he would be welcomed back if “for some reason things don’t work out.”

Trump’s first list of science priorities ignores climate—and departs from his own budget request

President Donald Trump has translated his campaign promise to “make America great again” into his administration’s first blueprint for federal investment in science and technology. This week, the White House issued a four-page memo telling federal agencies that their research dollars should be focused on delivering short-term dividends in strengthening national defense and border security, the economy, and “energy dominance,” as well as improving public health—in that order.