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.

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.

Death Valley’s 134°F reading from 1913 is still the official world heat record. A new study says the real high was about 120°F. Here is the case against it.

In 1858 a cable under the Atlantic carried messages for three weeks, set New York’s City Hall on fire in celebration, and then went dead. This is how it failed, and how the Great Eastern finally wired two continents together in 1866.

In 1868 astronomers saw a yellow line in the Sun that matched nothing on Earth. The story of helium runs from a forgotten observer in India to a Kansas gas well, a teacup of liquid at Leiden and the helium shortage of 2026.