The Night Sky Is Not Dark at All Frequency

It is not dark at all frequencies. If we shift to the right frequency, there's usually something coming from every point in the sky we look at. The interstellar gases are just thick enough to absorb enough of the radiation sent by more distant stars that we can't with our naked eyes see things all the way back to the dawn of time. So those mor distant and fainter lights do get filtered out by the dust. And so the night sky appears dark to us instead of appearing light.