This issue I will answer the first question. The second, which is much more difficult, will be answered next issue.

At any "dark" site, such as Chews Ridge, on a clear, moonless night, everything seems clearly illuminated to the dark-adapted eye. Even large print is legible. If you stretch out your hand against the sky, the fingers are all clearly silhouetted against the grey sky. How can this be true?

First, the sky light comes from two sources: the glow of the molecules in the atmosphere (mostly the green line of ionized oxygen) excited by the solar wind striking the upper atmosphere. This is sort of a weak version of the aurorae. The second source is the starlight itself, scattered by aerosols and molecules in the atmosphere. In the desert or over snow, the effect is more pronounced as the starlight reflects off the terrain and gets a second chance to scatter before returning to space.

Second, your eyes are well adapted to dark conditions. The rods in your retina (the sensitive, black and white sensors) are flooded with a chemical agent that sensitizes them. This takes about a half-hour and we generally know it as dark adaptation. It has been pointed out that the time needed for this to take effect is about the twilight interval.