Light Travel Time: How the Night Sky Shows Cosmic History
Why looking at distant stars and galaxies means observing light that began its journey long ago.
Astronomy · Time · The Unknown
Marvis Huff
Cosmos
Clear, carefully sourced essays about the scale of the universe—and the questions that begin when we look up.
Interactive cosmic distance lens
Distance is a view into the past.
Move through the scale of the observable universe. The farther the light has traveled, the earlier the moment we see.
Sunlight reaches Earth after about eight minutes.
8 minutesThe Sun
SunEarly universe
The observatory
Six journeys across space and time
Reading an Exoplanet Atmosphere in Starlight
How transmission spectroscopy helps astronomers investigate the atmospheres of planets orbiting other stars.
The Speed of Light: A Cosmic Speed Limit
What the speed of light means, why a light-year measures distance, and how relativity changes journeys near the cosmic speed limit.
TON 618: Measuring an Ultramassive Black Hole
How astronomers infer the extraordinary scale of TON 618, a distant quasar powered by one of the most massive black holes observed.
The Andromeda Galaxy: Our Nearest Major Galactic Neighbor
What Andromeda's ancient light reveals—and why its future encounter with the Milky Way is now considered uncertain.
The Search for Intelligent Life: From Possibility to Evidence
How scientists search for technosignatures while separating intriguing possibilities from confirmed evidence.