Various molecules, atoms and particulates float around in the air, and these reflect light ... A decently dark site in a rural area has a sky background of about 21 mag/arcsec 2.

One among those concepts is, “Why does the sky appear blue during ... white light from a spacecraft or the Moon. When we look away from the sun, there is nothing but the dark expanse of space ...

Earlier this year, in a letter to the journal Science, two American astronomers introduced a new term to capture the loss of our ability to observe the night skies due to light pollution.

Lemmon Sky Center during December 2011. LDN 1622 is called a dark nebula because interstellar dust is so thick it obscures light from nearby ... photo captures bright blue shock wave around ...