Why Is The Night Dark? Poem by Paul Hartal

This looks quite as a silly question.
The sun is down at night, that's why.
Yes, but actually on a clear starry night
the sky should be luminous like during the day.
Why? Because in the universe there are billions
of galaxies with trillions of stars. Many of these stars
are bigger and shine with brighter light
than our own sun.

So why is the night sky dark?
The paradox can be explained this way:
Numerous galaxies and their stars are so old
and so far away from us that their light still
did not reach us.
Another reason for the blackness of the night sky
is related to the expansion of the universe.
As the galaxies and stars move away from us
at extremely high speed, their lights
are stretched and transformed into infrared light
which transcends the visible spectrum and
therefore is imperceptible to the human eye.