A vacuum is defined as a space that
contains absolutely nothing, and it is often thought that the space between the
stars and galaxies constitutes a perfect vacuum.
However, this is not necessarily so. Within
every cubic kilometre of space there will be at least a few atoms of dust and
gas.
It has been discovered that interstellar
space (i.e. the space between our solar system and neighbouring stars) contains
atoms of hydrogen and helium as well as small amounts of dust. The proportion
of these is 90% hydrogen, 9% helium and 1% dust.
The dust comprises silicates (compounds of
silicon and oxygen), carbon and iron.
Intergalactic space contains minute amounts
of ionized hydrogen, by which is meant hydrogen nuclei from which their
electrons (one per atom) have been stripped away.
So space is not empty – just very nearly
so!
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