Re: Why is the dark part of a crescent moon visible at night?

Jeremy, you asked and answered your own question! :)

The dark area of the crescent moon is indeed lit by reflected
sunlight from the Earth. As a matter of fact, this effect is
known as "Earthshine". If you were an astronaut standing on
the nighttime side of the moon (and you were on the side which
always faces Earth!), then you could look into the pitch black
lunar sky and see the Earth as a little bluish-white globe up
above you: The Earth would appear to be about the width of two
of your fingers, held out at arms length. And it would appear
over thirty times brighter than the full moon does from Earth!

Obviously, with this monstrously bright Earth sitting in your
dark night-time sky, the lunar landscape all around you would
be bathed in gentle light - considerably more brightly than
the Earth's landscape is bathed in light during full moon. So
it's no wonder that "Earthshine" lights up the dark area of
the moon brightly enough that we can see it all the way back
here on Earth! What *is* amazing, though, is that Earthshine
can really only be seen during the Crescent phase of the moon.

During the Quarter Moon (when half the moon is illuminated as
seen from Earth), the bright side of the moon is so bright it
washes out the Earthshine: then the dark side of the moon does
SEEM very, very dark. But of course the moon's night-time sur-
face shines just as bright from Earthshine then as always!