Also note that the shadowed part of the moon is invisible to the naked eye in the diagram above, it is only shown for clarification purposes. At certain times we see both the sunlit portion and the shadowed portion - and that creates the various moon phase shapes we are all familiar with. Of course that is perfectly logical, but you need to visualize it in order to understand the phases. One important thing to notice is that exactly one half of the moon is always illuminated by the sun. When you do this, you'll 'see' that the illuminated portion is on your left, just as you see in the large image. For the waning gibbous, third quarter, and waning crescent phases you have to mentally turn yourself upside down when imagining the line of sight. The large moon image shows what you would see at that point in the cycle.

The dotted line from the earth to the moon represents your line of sight when looking at the moon. The moon phase name is shown alongside the image. The moon is shown at 8 key stages during its revolution around the earth. The earth, of course, is at the center of the diagram. Sunlight is shown coming in from the right. The illustration may look a little complex at first, but it's easy to explain.

Lunark name