A light-year is the distance light travels in one year, about 9.46 trillion kilometers. It is a unit of distance, not time, and it lets astronomers express the vast gulfs between stars in manageable numbers. The nearest star to the Sun, Proxima Centauri, lies 4.24 light-years away. Because light takes time to reach us, looking far out in space is also looking back in time: we see the most distant galaxies as they were billions of years ago.
Astrophysics · Supernovae · Black Holes
A star 730 million light-years away brightened for four years, exploded, then exploded again. No human flagged it. An algorithm built to find the stra...
Astrophysics · Neutron Stars · Multi-messenger Astronomy
In August 2025, a faint gravitational tremor and a fading point of light arrived together from 1.3 billion light-years away. Astronomers had theorized...
Astrophysics · Solar Neighborhood · Supernovae
A thousand light-years across, the Local Bubble is a cavity blown into the galaxy by a string of ancient supernovae. Our solar system is drifting thro...
Cosmology · Large-Scale Structure · Voids
In 1981, a redshift survey turned up an emptiness so vast that if the Milky Way sat at its center, we might not have learned other galaxies existed un...
Astrophysics · Supernovae · Magnetars
A billion light-years away, one of the brightest explosions in the universe pulsed with a rhythm that kept speeding up. That accelerating beat, astron...
Astrophysics · Black Holes · Galactic Center
Sagittarius A* is a supermassive black hole 4.3 million times the mass of the Sun, sitting 27,000 light-years from Earth. For three decades it was an ...