The Solar System & Phases of the Moon

New Moon

• The new moon occurs when the moon is between the sun and the earth. The portion of the moon that is illuminated is faced away from earth in this phase, so the moon appears dark from earth. As the new moon continues its orbit, it passes through the waxing crescent phase. A small sliver of the moon is illuminated during this phase and it can be seen best just after sunset.

First Quarter Moon

• A first quarter moon occurs when the sun and moon are perpendicular, which allows sunlight to illuminate half of the side of the moon seen from earth. People viewing the moon at this phase will see half of the moon illuminated and the other half still in darkness. Continuing on its orbit, the moon passes through the waxing gibbous phase. At this phase, more than half of the moon appears illuminated from earth.

Full Moon

• During a full moon, earth is directly in between the sun and the moon. The moon is fully illuminated and can be seen in the night sky for most of the night. The next transitional phase is known as the waning gibbous phase. This phase occurs in reverse of the waxing gibbous phase. First, all but a small sliver of the moon is visible. As the moon progresses toward the next phase, the dark sliver gets larger.

Last Quarter

• The last quarter phase of the moon occurs when the moon and sun are again perpendicular. Half of the moon is illuminated during this phase, but it is the half that was dark during the first quarter that is illuminated this time. As the moon continues to orbit, sunlight reaches less and less of the surface facing earth, resulting in the dark half growing larger until only a sliver of the moon is illuminated. When the moon completes its orbit, it enters into the new moon phase once again.