Each month has eight moon phases in 2013 as it does every year. These eight phases are easily predictable. The phases of the moon are the new moon, waxing crescent moon, first quarter moon, waxing gibbous moon, full moon, waning gibbous moon, last quarter moon, and the waning crescent moon. NASA has a schedule of the moon phases 2013, as well as for a period of 6,000 years at this link.
What Is A Moon Phase?
Each phase of the Moon is referred to as a lunar phase. A lunar phase is the illuminated portion of the Moon as it is perceived from Earth. The phases change as the Moon orbits Earth. A portion of the Moon is illuminated at all times, except during a total lunar eclipse. The lunar phases are each called a syzygy. Syzygy is the term used when any three celestial bodies become aligned. With our Moon, the three bodies involved are the Sun, Moon, and Earth. The recurrence of a lunar phase can be easily predicted. Each phase returns every 29 days, 12 hours, and 44 minutes. This is called the synodic month. The difference between our calendar months and the synodic month explains why occurrence of the phases of the Moon varies from month to month.
Description Of The Lunar Phases
During a New Moon it seems as if there is no moon at all in the night sky because the illuminated portion is facing the Sun. The Moon has its back to Earth. A solar eclipse can only happen during a new moon. If you are in a very dark area, away from city lights, you can see a phenomenon called earthshine during a new moon. Earthshine is actually the light from the Sun being reflected by the Earth.
The Crescent Moon is the leading portion of the Moon. In the northern hemisphere, this is the right side of the Moon, but if you are in the southern hemisphere, it would be the left side.
The First Quarter moon is actually half of the illuminated hemisphere. During this phase, the Sun and Moon are at a 90 degree angle to Earth.
The Waxing Gibbous allows Earth-based observers to see more than half of the illuminated hemisphere of the Moon as it moves into its full phase.
The Full Moon is the brightest phase. This is the only phase when a lunar eclipse can happen. A lunar eclipse happens when the Moon passes through the Earth’s shadow.
During the Waning Gibbous moon, more than half of the Moon is visible as it is moving toward the last quarter and eventually into a new moon.
The Last Quarter only half of the Moon is illuminated. The last quarter sees the opposite portion of the Moon illuminated when compared to the first quarter. So, in the northern hemisphere, the left side of the Moon is seen and the right side is seen in the southern hemisphere.
That takes us to the Waning Crescent Moon. Only a small sliver of the Moon can be seen as it turns its dark side toward Earth once again.
It may also interest you to know how often a solar or lunar eclipse can occur. NASA has found a formula that accurately predicts when either will occur. Here is a link to a NASA webpage that explains the entire process and how the formula was derived.