Lunar node

A lunar node is either of the two orbital nodes of the Moon, that is, the two points at which the orbit of the Moon intersects the ecliptic. The ascending (or north) node is where the Moon moves into the northern ecliptic hemisphere, while the descending (or south) node is where the Moon enters the southern ecliptic hemisphere. Motion The Moon crosses the same node every 27.2122 days, an interval called the draconic month (or draconitic month). The line of nodes, the intersection between the two respective planes, has a retrograde motion: for an observer on Earth, it rotates westward along the ecliptic with a period of 18.6 years or 19.3549° per year. When viewed from the celestial north, the nodes move clockwise around Earth, opposite to Earth's own spin and its revolution around the Sun. Because the orbital plane of the Moon precesses in space, the lunar nodes also precess around the ecliptic, completing one revolution (called a draconic period or nodal period) in . (This is not the same duration as a saros.) The same cycle measured against an inertial frame of reference, such as International Celestial Reference System (ICRS), a coordinate system relative to the fixed stars, is 18.599525 years. Eclipses