Today, the Moon, second brightest object in the sky, has reached the First Quarter phase, which means that it is exactly 270 degrees around its orbit of Earth and is three quarters finished with its current orbit..
As for lunar mechanics, the Moon is always half lit. The reason we don't always see it as such is thanks to orientation in relation to us. Right now, with the Moon at a 90 degree angle relative to the Earth-Sun line, we only see half of the lit side.
After today, we will see even less of the Moon each night as its lit side turns more away from us and heads toward New in a week.