You're an ill-informed English major. You instructed me to call you that, so I did.
The light source for this image is the Sun.
"The dark side of the moon" is a phrase that seems to have a strange effect on people; they seem to use that phrase to incorrectly mean the far side of the moon, and then that puts the idea in their heads that the far side is always dark. It isn't; the far side is fixed, the dark side is constantly changing.
The Moon is tidally locked to Earth, this means the moon's rotational speed and its orbital period are the same, the moon rotates once on its axis for every one orbit of the Earth it performs, meaning it doesn't (significantly) rotate when seen from Earth. No human saw the far side of the moon until the Soviets flew a satellite around it, and only 27 men and 1 woman have ever seen it with their own eyes. Until this week, those numbers were 24 and 0.
It is hidden from us but not from the Sun; we observe the Earth waxing and waning, being full and then half a month later being new. When the moon is new, the near side is in darkness and the far side is in light. On the Lunar surface, a day and night takes an entire month, while the continents and oceans of the Earth hanging still in space overhead whirl past nearly 30 times.
Finally...the image above isn't the whole far side. About half of the near side is visible; the big dark patch to the right is the Ocean of Storms, most of the Sea of Rain is visible as well. Kepler and Copernicus crater are visible, Tycho is just out of shot, if you look closely you can just barely see one of Tycho's rays across the Sea of Clouds. That one very dark patch just right of center is Grimaldi crater. All those features are visible from the Earth, in fact two of the Apollo landing sites are visible here, 12 and 14. The very large carter, the dark patch to the left of center of the image is Mare Orientale, which is just barely visible on the edge of the Moon from Earth, from our point of view it's on the "side". It's eastern ridge is visible from Earth but we don't really see the dark mare itself.
