Photography : Astronomy : Old Moon in the New Moon's Arms
When the Moon is "young", only a few days after being new, you can actually see features on the dark side even though it's not lit up by the Sun. What's lighting up the Moon? The Earth! This faint glow is called "Earthshine" because it is light from the Sun reflecting off the Earth and shining on the Moon. I even caught a star in this shot. According to how Stellarium says the sky was when I took this picture, that is probably 44 Aqr, a supergiant 340 light years away in the constellation Aquarius
We see the Moon go through phases because the Moon is lit up from different angles, even though we see the same side of the Moon (more or less). As the Moon orbits the Earth, the Sun is lighting it from different angles, so the light falls on different parts of the Moon. When the lit half faces the Sun, we only see the dark side and call it a New Moon. When we see half of the lit side, we call it a Quarter Moon. When we see all of the lit side, we call it a Full Moon.