Outer

Outer Space

Outer space, also known as space, is the expanse that exists beyond the Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays.

Overview

The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvin (−270.45 °C; −454.81 °F). The plasma between galaxies accounts for about half of the baryonic (ordinary) matter in the universe; it has a number density of less than one hydrogen atom per cubic meter and a temperature in the range of 10 million to 100 million kelvin.

Exploration

The exploration of outer space is carried out by astronomers with telescopes and also by spacecraft. The study of outer space has led to significant discoveries and a broad understanding of the cosmos.

Legal status

The Outer Space Treaty provides the basic framework for international space law. It bans the stationing of weapons of mass destruction in outer space and restricts the use of the Moon and other celestial bodies to peaceful purposes.

See also

• Astronomy
• Cosmology
• Space exploration
• Spacecraft propulsion
• Space weather