The boundaries between
the Earth's surface and outer space, at the Kármán line, 100 km (62 mi) and
exosphere at 690 km (430 mi). Not to scale.
Outer space, or simply
space, is the void that exists between celestial bodies, including the Earth.
It is not completely empty, but consists of a hard vacuum containing a low
density of particles: predominantly a plasma of hydrogen and helium, as well as
electromagnetic radiation, magnetic fields, and neutrinos. Observations and
theory suggest that it also contains dark matter and dark energy. The baseline
temperature, as set by the background radiation left over from the Big Bang, is
only 3 Kelvin (K); in contrast, temperatures in the coronae of stars can reach
over a million Kelvin. Plasma with an extremely low density (less than one
hydrogen atom per cubic meter) and high temperature (millions of Kelvin) in the
space between galaxies accounts for most of the baryonic (ordinary) matter in
outer space; local concentrations have condensed into stars and galaxies.
Intergalactic space takes up most of the volume of the Universe, but even
galaxies and star systems consist almost entirely of empty space.
There is no firm
boundary where space begins. However the Kármán line, at an altitude of 100 km
(62 mi) above sea level, is conventionally used as the start of outer space for
the purpose of space treaties and aerospace records keeping. The framework for
international space law was established by the Outer Space Treaty, which was
passed by the United Nations in 1967. This treaty precludes any claims of national
sovereignty and permits all states to explore outer space freely. In 1979, the
Moon Treaty made the surfaces of objects such as planets, as well as the
orbital space around these bodies, the jurisdiction of the international
community. Additional resolutions regarding the peaceful uses of outer space
have been drafted by the United Nations, but these have not precluded the
deployment of weapons into outer space, including the live testing of
anti-satellite weapons.
Humans began the
physical exploration of space during the twentieth century with the advent of
high-altitude balloon flights, followed by the development of single and
multi-stage rocket launchers. Earth orbit was achieved by Yuri Gagarin in 1961
and unmanned spacecraft have since reached all of the planets in the Solar
System. Achieving orbit requires a minimum velocity of 28,400 km/h (17,600
mph); much faster than any conventional aircraft. Outer space represents a
challenging environment for human exploration because of the dual hazards of vacuum
and radiation. Microgravity has a deleterious effect on human physiology,
resulting in muscle atrophy and bone loss. As of yet, space travel has been
limited to the vicinity of the Solar System; the remainder of outer space
remains inaccessible to humans other than by passive observation with
telescopes.
From Wikipedia, the
free encyclopedia
IMAGES OF OUTER SPACE
Will outer space city look like this? |
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