CosmosObservatory
Explore
Solar System
Live
Learn
Tools
About
Cosmos Observatory
ToolsAbout
Cosmos Observatory

Explore the universe through NASA data, real-time ISS tracking, Mars rover imagery, asteroid monitoring, and comprehensive space encyclopedia. Your gateway to the cosmos.

Explore

  • APOD
  • Mars Rovers
  • Earth Imagery
  • NASA Gallery
  • ISS Tracker

Data

  • Asteroids
  • Solar System
  • Exoplanets
  • Space Weather
  • Launches

Tools

  • Glossary
  • News
  • Calculators

Legal

  • About
  • Privacy Policy
  • Terms of Use
  • Space Tools
  • Contact

Stay updated with the cosmos

Get weekly digests of APOD highlights, upcoming launches, and space events.

© 2026 Cosmos Observatory. All rights reserved. Built with for space enthusiasts.

This website is not affiliated with, maintained, authorized, endorsed by, or in any way officially connected with NASA or any of its subsidiaries or affiliates. All NASA imagery is in the public domain unless otherwise noted. Data sourced from NASA Open APIs, Launch Library 2, and other open data services.

  1. Home
  2. Glossary
  3. Event Horizon
Astrophysics

Event Horizon

Definition

The boundary around a black hole beyond which no light or radiation can escape. Once matter crosses it, it is inevitably pulled toward the singularity. The size depends on the black hole's mass and is described by the Schwarzschild radius.

Related Terms

Black Hole

A region of spacetime where gravity is so strong that nothing, not even light, can escape once past the event horizon. B...

Singularity

A point where matter density and spacetime curvature become infinite, as predicted by general relativity. Singularities ...

Accretion Disk

A rotating disk of gas, dust, and other matter that forms around a massive body such as a black hole, neutron star, or y...

Explore Related Topics

Dive deeper into event horizon and related concepts on Cosmos Observatory.

Solar System Explorer

See astrophysics in action across our solar system.

Exoplanet Explorer

Discover worlds beyond our solar system.

Full Glossary

Browse all 66+ space and astronomy terms.

Back to Glossary