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Why do NASA's New Moon dates not agree with WLC's?

Question: I have checked the dates of the New Moons at NASA, and have found that NONE of the "New Moon" dates agree with WLC.  Can you please explain why there is this difference?

Answer: The perceived discrepancy here is due to a misunderstanding of calendation terms.  The "Astronomical New Moon" and "New Moon Day" are not synonymous.

(1) Astronomical New Moon - The Astronomical New Moon is often referred to by astronomers simply as the "New Moon" or as the "Conjunction."  During the Astronomical New Moon, the moon's unilluminated side is facing the Earth. The moon is not visible (except during a solar eclipse). (http://aa.usno.navy.mil/faq/docs/moon_phases.php)

(2) New Moon Day - New Moon Day commences at the first dawn after the "Astronomical New Moon [Conjunction]" has occurred.  This means that the Astronomical New Moon and New Moon Day will always be one calendar date apart for any specified area.  For example: If the Astronomical New Moon (Conjunction) occurred at 12 pm on December 2 in your area, then New Moon Day would commence at dawn on December 3.  For more on this important topic, see New Moon Day: The Dawn After Conjunction.