Although this question is answered, I will say this: the orbital plane of moon is not in the same orbital plane of earth, there is about 5 degrees of inclination.
Example, if earth and sun was in the floor of a room, then the moon is on the opposite of sun, but raised from the floor . Now since sun is larger than the earth, the umbra of the shadow cone is diminishing behing the earth, see here: http://celestrak.com/columns/v03n01/fig-1.gif
Usually the moon is also outside the Pen-Umbra zone. That is why the mon gets illuminated, even being at the opposite side of sun (looking from top). Sometimes however, the moon, while in the opposite side of sun wrt earth, stays in the ascending or descending node, that is called a lunar eclipse.