What follows is a condensed and updated version of an online essay by Brian Skiff about the darkness of the night sky. It has circulated among amateur observers on the Internet since the early 1990s. Here is the original essay revised and updated by Skiff, with live links to background information and scientific literature cited. —Daniel Pendick
How dark can the night sky get?
Many people think of darkness as simply the lack of light, but actually there's a lot more to it than that.