The Moon Phases as viewed from Earth
An easy way to remember the phases of the moon is to think of "DOC"! On the first night of the lunar month ("moonth") the moon is not visible, this phase is called the new moon. The sun is shining on the back side (what we call the "dark side" of the moon) which can't be seen from our vantage point. We always see the same side of the moon because it rotates so slowly the same face is always toward the Earth, fortunately, the side we see is the prettiest! In 3 days a tiny sliver of a waxing crescent can be seen, this is the "D" in "DOC". Every night more light is added on the right side (waxing), making more of the moon's disc visible. One week into the lunar cycle half of the moon is visible (but it is called the 1st Quarter). This is the best phase to view the moon with binoculars or a telescope because it can be seen early in the evening and the craters are well defined by the shadows. It is often possible to see the moon during the afternoon in this phase. On day 12 the moon is almost, but not quite, full. This is the waxing gibbous phase. Two weeks into the moon's revolution around the earth we enjoy a big, bright full moon, the "O". Up until this point, the moon has had more light added each night, from here on out, there will be less light each night. By day 16 the light begins to wane to the right and the moon is in the waning gibbous phase. Day 21 brings the 3rd Quarter phase when the other half is seen. The moon rises an hour later each night, by day 26 only a tiny crescent is visible early in the morning, this is the "C" phase. On Day 28 the moon has completed its cycle.
The rare times that there are 2 full moons in one month, it is called a "Blue Moon".