The moon’s phases change over a lunar month, which is 29.5 days due to the earth’s movement. The moon’s illumination comes from the sun, and its visible shape changes as it revolves around the earth. There are eight phases in a lunar cycle, starting with the New Moon, which occurs when the moon is between the earth and sun. The moon’s visible shape changes until it reaches the Full Moon, then it starts to wane until it becomes the New Moon again.
The phases of the moon refer to the change in the aspect of the moon over the course of a lunar month. A lunar month is the time it takes for the moon to complete one revolution around the earth. A lunar month is 27.3 days, but the simultaneous movement of the earth around the sun makes the moon appear to take two days longer, about 29.5 days.
The moon receives its illumination from the sun. The side facing the sun is the lighted one and the side facing the sun is in the dark. Only the bright part of the moon is visible from the earth. During a lunar cycle, as the moon revolves around the earth, the bright part of the moon is viewed from different angles from the earth. This makes it appear that the moon is changing shape.
Eight phases of the moon occur in one lunar cycle. They are New Moon, Waxing Moon, First Quarter Moon, Waxing Gibbous Moon, Full Moon, Waning Gibbous Moon, Last Quarter Moon, Waxing Moon and New Moon. The phases of the moon keep repeating in an endless cycle, but since this cycle lasts 29.5 days, the phases of the moon do not occur on the same days each month.
The New Moon is the first of eight lunar phases. It is the result of the moon coming between the earth and the sun. The sunlit side of the moon is away from the earth, the dark side faces the earth, and therefore there appears to be no moon in the sky. The moon then changes position and a sunlit sliver of it becomes visible from the earth. This is the Crescent.
When half of the moon is visible, it is the first quarter moon. At this time the moon has completed a quarter of its revolution around the earth. When more than half of the moon becomes visible, it is the waxing moon.
The Crescent Gibbous waxes or grows, and finally the entire sunlit disk of the Full Moon makes its appearance. It is the only phase in which the moon is visible in the sky throughout the night. At a full moon, the moon completes half of its revolution around the earth.
As the moon begins the next half of its revolution, the portion of the moon visible from earth begins to thin out. The full moon wanes and the sliver of darkness of the waning gibbous moon appears. When half of the moon goes dark, it is the last quarter moon. This turns into the bright sliver of the Waxing Moon and finally total darkness with the New Moon.
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