I would like to first clarify - the
temperature of space is not quite absolute
zero, meaning zero on the Kelvin scale,
written as 0 K. This temperature is equivalent
to -273.15 degrees Celsius, and -459.67 degrees
Absolute zero is defined as the temperature
at which there is essentially no movement from any
particle, translational (moving in space
up/down, left/right, forward/back) or vibrational
(vibrating in place).
The baseline temperature of space, in other
words the background temperature of space, is
technically 2.7 K, which is still very low
compared to any natural temperatures we deal with!
This temperature is measured as the temperature
of the background radiation in space from the Big
Bang. This background radiation is radiation
that cannot be assigned to any source that we know
of such as stars, etc. You can think of this
radiation as a kind of "leftover" from the Big
Bang. Apart from this radiation, there is not
a lot of movement of any kind in outer space,
partly because there are very few particles per
In interstellar space, the space between star
systems in a galaxy, there are only a few hydrogen
atoms per cubic feet in the least dense areas!
That's why space is so cold - temperature,
as we know it, is just a measurement of how fast
very small things (the particles that make up
everything) move on average, and there are just
not many things in the regions of space not near
stars, planets, or other types of objects. Hope
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