Dark energy accounts for 68% of the universe's total mass-energy, but it was only discovered in 1998, through the light of distant exploding stars.

The star pattern most people call the Big Dipper is not actually a constellation, but an asterism borrowed from Ursa Major, and its familiar shape is slowly drifting into a new one.

Auroras are older than written history and stranger than postcard photos suggest, from a purple impostor named Steve to a light show on Jupiter that never turns off.

The astronomical unit, once just an average of Earth's distance from the Sun, is now a fixed number by international decree — the product of a centuries-long hunt that ran through ancient geometry, a rare planetary crossing, and a passing asteroid.

From a planet nearly Saturn's size with only about twice Earth's mass to worlds spotted beyond our own galaxy, exoplanets keep rewriting what a planet can be. Here is what verified sources say.

A total solar eclipse can take centuries to revisit the same spot on Earth, yet its few minutes of totality have rewritten physics, exposed the Sun's hidden atmosphere, and been recorded by sky-watchers for over a thousand years.

Sagittarius A* is the supermassive black hole anchoring the Milky Way, first photographed in 2022 and weighing 4.297 million times as much as the Sun.

Proxima Centauri b is the nearest exoplanet to Earth, orbiting a small red dwarf star roughly 4.2 light-years away. Confirmed in 2016, it sits in the destination system of a proposed interstellar light-sail mission.

Kepler data points to roughly 40 billion Earth-sized worlds that could sit in the temperate zones of stars scattered across the Milky Way. Here is what actually decides whether a planet belongs there.

Vega has spent two centuries as astronomy's favorite test subject, racking up firsts from the earliest stellar photograph to the first dust disk ever found. This is the story behind that streak.

A space telescope once spotted a genuine hole in the sky, and that is only one of the surprising facts behind how stars are born, classified, and eventually fade away.

Proxima Centauri is our Sun's nearest stellar neighbor, yet you will never spot it without a telescope. Here is what makes this small red star, and its planets, so remarkable.