A light-year is not a measure of time at all — it's a fixed distance of trillions of kilometres, and most working astronomers reach for a different unit anyway.

Dark matter was named decades before anyone found real evidence for it, and today it's thought to make up more than a quarter of the universe. Here's what the evidence actually shows.

Sirius outshines every other star in Earth's sky, but its real surprise is the crushed, Earth-sized ember hiding beside it. Here's how astronomers tracked it down, and why a record-setting aircraft once borrowed its name.

Voyager 2 remains the only spacecraft ever to visit Uranus and Neptune, a detour made possible by a planetary alignment that occurs only once every 176 years. Launched in 1977, it is now NASA's longest-running mission and has been sailing through interstellar space since 2018.

From a 1929 sketch of a spinning wheel to China's Tiangong, space stations have quietly rewritten the record books for how long humans can live off Earth.

In medieval Paris, teaching that other universes could not exist was grounds for excommunication; today physicists search the sky for actual evidence of them.

The James Webb Space Telescope is the largest observatory ever placed in space, and it does its work from a lonely orbit far beyond the Moon. These are the numbers behind the mission.

The International Space Station has never sat empty since November 2000, housing crews in quarters bigger than a six-bedroom house while circling Earth every 90 minutes.

Hubble launched with a flawed mirror, got fixed by astronauts on five shuttle missions, and went on to photograph galaxies from 13.2 billion years ago.

Falcon 9 has flown 660 successful missions and turned rocket landings from a coin-flip gamble into routine business. Here's how SpaceX rebuilt the economics of getting to orbit.

The zodiac started as a precise Babylonian measuring system, not a personality quiz — and more than two millennia of Earth's slow wobble have since pulled the constellations out from under the signs named after them.

Newton's law of gravity predicted a planet and explained falling apples, but it left a small, stubborn gap in Mercury's orbit that took Einstein's general relativity to close. Here is what the historical record shows about the force that never lets go.