A Swedish chemist’s dazzling green ended up on Victorian walls, gowns, sweets and book covers. It was made with arsenic. Here is how the craze spread, who paid for it, and why libraries are still checking their shelves.

In 1936 Danish seismologist Inge Lehmann used faint waves from a New Zealand earthquake to find a core within Earth’s core. Nearly a century later, that iron heart is still surprising scientists.

Harry Houdini spent his last years exposing fraudulent spirit mediums, from Conan Doyle’s séances and the Margery case to Congress. A century later, the science of why we get fooled.

A century after her thesis, a London blue plaque honors the astronomer who found that stars are mostly hydrogen and helium, and the famous astronomer who told her it was impossible.

Henrietta Swan Leavitt found the Cepheid law that first measured distances to other galaxies. A century later, astronomers rechecking her handwritten data say it holds up remarkably well.

In 1961 a converted barge off Mexico drilled into the deep ocean floor for the first time, the opening move in Project Mohole, a Cold War plan to drill through Earth’s crust to the mantle. Mohole collapsed in politics and cost overruns, but the ocean drilling it spawned proved plate tectonics, found a dried-up Mediterranean and, 65 years on, is still chasing the Moho.

Minutes before the first Moon landing, the computer flying Apollo 11’s lunar module began flashing a 1202 alarm. The story of that machine, its programs woven by hand into core rope, and the MIT team led by Margaret Hamilton whose software knew what to drop and kept flying.

In June 1783 a crack opened in the Icelandic highlands and poured out lava and poison gas for eight months. The famine that followed killed a sixth of Iceland, a stinking dry fog spread over Europe, and Benjamin Franklin guessed what it meant.

For 130 years, the kilogram was a golf-ball-sized cylinder locked in a vault near Paris. Then it seemed to start losing weight, and scientists spent four decades learning to weigh with electricity and count atoms to replace it.

In a Montreal operating room, a surgeon touched a wire to the brains of awake patients and asked what they noticed. Their answers gave neuroscience its most famous map, and one of its most stubborn myths.

In 1848 a tamping iron passed through the head of a Vermont railroad foreman. He lived, he changed, and then he quietly got better. The true story of Phineas Gage is stranger than the textbook version.

On March 1, 1954, a miscalculated hydrogen bomb at Bikini rained radioactive ash on Marshall Islanders and a Japanese tuna boat, and changed the nuclear age.

On August 15, 1977, a volunteer circled six characters on a radio telescope printout and wrote Wow! beside them. Nearly 50 years of searches, failed theories and a new look at the old paper later, here is what the Wow! signal was, and what it might have been.

Ranked by erupted magma volume, North America’s five largest eruptions of the past 2.6 million years, from Valles caldera to Yellowstone’s Huckleberry Ridge, and what their calderas and ash beds reveal about how supervolcanoes work.