Assuming you're asking how often a "half moon" appears, a half moon (First or Third Quarter moon) will usually occur every 14-15 days (half a lunar month).
because the moon is one quarter size of the earth.
The first quarter appears as a phase of the Moon when half of its illuminated side is visible from Earth. This occurs about a week after the new moon, when the Moon has moved a quarter of the way through its orbit around Earth. The sunlight is hitting the Moon at a right angle, which creates the half-lit appearance. This phase is often associated with growth and progression in lunar cycles.
First quarter and last quarter appear as a half moon. about halfway down this page are some pictures: http://www.calculatorcat.com/moon_phases/moon_phases.phtml
At the time of the "First Quarter" and "Third Quarter" phases, the moon appears half-illuminated. These occasions are roughly 7 days and 21 days after New Moon respectively, and Full Moon occurs at the time exactly midway between them. Note: Both phases are easily visible in the daytime. First Quarter rises in the east around Noon, and Third Quarter sets in the west around Noon.
The four phases of the moon that appear to last 1 or 2 nights are the New Moon, First Quarter, Last Quarter, and Full Moon. The New Moon and Full Moon both occur for one night, while the First Quarter and Last Quarter phases can last for about one to two nights.
The phases called "first quarter" and "third quarter" have those labels because theyoccur one quarter and three quarters of the period of time from one new moon untilthe next new moon.At both of those times, we see half of the moon lit up.
Half of it, the same as always. Half of the visible side of the Moon will be brightly lit by the Sun, and the other half is often dimly visible by reflected earthshine, sunlight that is reflected from the Earth and then shines down on the night side of the Moon.
The four main phases of the moon are New Moon, First Quarter, Full Moon, and Last Quarter. These phases occur as the moon orbits Earth and changes position relative to the sun, causing different portions of the moon to appear illuminated from our perspective.
If the moon is full today, in a week it will be in the last quarter phase. The lunar cycle progresses from full moon to last quarter over approximately a week, as the moon moves into a waning phase. This means it will appear as a half-moon, with the left side illuminated in the Northern Hemisphere.
A half moon appears when only half of the moon's illuminated side is visible from Earth. This occurs when the moon is at a 90-degree angle relative to the Earth and the sun, known as the first quarter or third quarter moon.
The four faces of the moon are called the Phases of the Moon. They are the New Moon, First Quarter, Full Moon, and Last Quarter.
Both the 1st Quarter moon and the 3rd (last) Quarter moon can be referred to as the "half moon" since we see half of the sunlit side of the moon.