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.

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.

How two feuding 19th-century scientists, Edward Drinker Cope and Othniel Charles Marsh, bribed, spied and raced to fill America with dinosaurs.

A late moon of Jupiter, a toothed wheel, a mirror spinning 528 times a second and a mile of pipe: the 300-year race to measure the speed of light.

A sickly French road engineer cut away the glass a lens doesn’t need and made lighthouses shine to the horizon. His idea still lights stages, cars and VR headsets.

The deadliest disaster in U.S. history wiped out Galveston in one night in 1900. Then the city built a seawall and jacked itself up as much as 17 feet.

In 1835 the New York Sun reported that John Herschel had seen bat-winged people on the Moon. The story behind the Great Moon Hoax, and the optics that rule it out.

A B-52 on a secret radar-watching mission caught fire over Greenland in 1968 and crashed with four H-bombs. What followed: a cleanup in the polar night, a hunt for a lost bomb core and a scandal in Denmark.

A nuclear-powered Army town carved into the Greenland ice, a secret missile plan, and a few jars of forgotten mud that rewrote the history of the ice sheet.

A plate tossed in a Cornell cafeteria, a Nobel Prize, a famous mistake, and the same equation that makes the whole Earth wobble.