outerspace

Outer space, or space, is the expanse beyond Earth's atmosphere. It is commonly said to begin at the Kármán line, about 100 kilometers (62 miles) above sea level, though there is no universally fixed boundary. Space extends from there to the solar system and beyond into the observable universe.

Space is a near-vacuum with extremely low particle densities. It features microgravity, solar and cosmic radiation, and extreme temperature variations. There is no atmosphere to scatter light, so the sky is dark and celestial objects are visible even during daylight in orbit.

It contains natural bodies—planets, moons, asteroids, and comets—and human-made objects such as satellites, probes, and space stations. The space between objects contains solar wind, dust, and sparse plasma, while the broader universe includes stars, galaxies, and cosmic background radiation.

Space exploration and science are conducted by many space agencies and researchers. Human spaceflight began in the 20th century, with orbital missions and later landings on the Moon. Space-based observatories and probes advance our understanding of astronomy, planetary science, and the origins of the universe.

Hazards in space include radiation exposure, micrometeoroid impacts, and debris from previous missions. Space activity requires specialized technology and international coordination to ensure safety, reliability, and sustainable use of orbital regions.