Knowra Outer space Outer space Outer space is the region beyond Earth’s atmosphere, containing celestial objects and the sparse matter and radiation between them. It is not a perfect vacuum.
Kármán line : A proposed boundary about 100 kilometers above Earth, often used to mark the start of space. It provides a widely used, though not universal, altitude for defining where space begins.
Gravity : The attraction between matter and energy described by general relativity and approximated by Newtonian mechanics. Gravity gathers matter into stars and galaxies while shaping the motion of celestial objects.
Spaceflight : The use of vehicles to travel beyond Earth's atmosphere or move through space. Spaceflight is the practical means of reaching and operating in outer space.
Big Bang : The early hot, dense state and subsequent expansion that describe the observable universe's history. It is the leading cosmological account of the universe's early evolution.
Low Earth orbit : An Earth orbit with an altitude generally between about 160 and 2,000 kilometers. It is a nearby region of space with distinct orbital conditions and frequent satellite traffic.
Earth's atmosphere : The layer of gases surrounding Earth, held by gravity and becoming gradually thinner with altitude. Its gradual transition into space makes any boundary between atmosphere and space conventional.
General relativity : Einstein's theory describing gravity as the curvature of spacetime caused by matter and energy. It explains how matter and energy curve space and alter the passage of time.
Artificial satellite : A human-made object placed in orbit around Earth or another celestial body. Satellites use space for communications, navigation, weather observation, and scientific measurement.
Cosmic inflation : A hypothesized brief episode of extremely rapid expansion in the very early universe. Inflation may explain the universe's large-scale uniformity and the seeds of its structure.
Geostationary orbit : A circular equatorial orbit in which a satellite's period matches Earth's rotation, appearing fixed in the sky. It contrasts low Earth orbit through its altitude, period, and continuous view of one region.
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