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The Crescent Moon refers to two phases of the Moon. The waxing crescent is the lunar phase in which the first 1-49% of the Moon is visible in the night sky. The waning crescent is when the receding 1-49% of the Moon can be seen.
In 2010 the waxing crescent Moon will begin on Jan 10th, Feb 8th, Mar 8th, April 8th, May 8th, June 6th, July 6th, Aug 5th, Sept 3rd, Oct 3rd, Nov 2nd, and December 1st. The waxing crescent lasts for approximately seven days before the first quarter of the Moon is complete.
The waning crescent, in 2010, begins on Feb 7th, March 5th, April 6th, May 6th, June 4th, July 4th, August 3rd, September 1st, October 1st, October 30th, November 28th, and December 28th. This lunar phase also lasts approximately seven days.
The lunar phases vary in a continuous cycle as the Moon orbits the Earth and in relation to the changing positions of the Sun, Earth, and the Moon itself. One half of the Moon’s surface is always illuminated by the Sun(not withstanding eclipses). What truly varies is the portion of the illuminated hemisphere that is visible to an observer.
Looking at the dates for the waxing and waning crescents, you will notice that they change by about 1 day per month. The reason for that is the calender month and the Moon’s synodic(phase) cycle repeat at slightly different times. The calender month last 30.44 days. The Moon’s phases repeat every 29.53 days. This difference in actual cycle times accounts for the differing start days for the Moon’s phases.
This also accounts for the rare ‘blue moon’. A blue moon is the third full moon during a season or the second full moon in one month.
The Moon was playing an important role in many societies long before recorded history. Since man began to study when to plant crops or to impregnate women, the Moon has been the focal point. Some ancient rituals would begin with the crescent moon and culminate at the full moon. The romance of the Mon has been ever alluring.
We’ve also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.