The new moon was four days ago, on January 16. The synodic period (the amount of time between full moons, or new moons or whatever) is 29 days, 12 hours, and about 44 minutes. The sidereal orbit (the orbit around the earth without regard to the relative position of the sun) is a little more than two days shorter than that, of course. In the time it takes the moon to circle the earth, the earth has moved almost one twelfth of the way around the sun and it takes the moon that extra two-plus days to get back into the same position relative to the sun and the earth. During the first quarter of the cycle, the moon is a growing (waxing) crescent (less than half visible). The second quarter it is waxing gibbous (more than half visible).