draconic month

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The mean interval of time between successive passages of the Moon through the ascending node of its orbit, the point at which it passes from south to north of the ecliptic; also known as a nodical month. The Moon's orbit is inclined at about 5° to the ecliptic but it is not fixed in space. It has a slow variation which causes the two nodes to regress around the ecliptic every 18.61 years. Consequently the draconic month (27.2122 days) is about 2.5 hours shorter than the sidereal month.

Subjects: Astronomy and Astrophysics.

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