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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.
The Moon completes one orbit around the Earth in 27.32166 days. The two points at which the Moon crosses the ecliptic are known as its orbital nodes, shown as "N1" and "N2" (ascending node and descending node, respectively), and the line connecting them is known as the line of nodes.
In the case of objects outside the Solar System, the ascending node is the node where the orbiting secondary passes away from the observer, and the descending node is the node where it moves towards the observer. [5], p. 137. The position of the node may be used as one of a set of parameters, called orbital elements, which
An eclipse of the Moon or Sun can occur when the nodes align with the Sun, roughly every 173.3 days. Lunar orbit inclination also determines eclipses; shadows cross when nodes coincide with full and new moon when the Sun, Earth, and Moon align in three dimensions. In effect, this means that the "tropical year" on the Moon is only 347 days long.
As a result of this nodal precession, the time for the Sun to return to the same lunar node, the eclipse year, is about 18.6377 days shorter than a sidereal year. The number of solar orbits (years) during one lunar nodal precession period equals the period of orbit (one year [ specify ] ) divided by this difference, minus one: 365.2422 / 18 ...
The period for the Sun to return to a node is called the eclipse or draconic year: about 346.6201 days, which is about 1 ⁄ 20 year shorter than a sidereal year because of the precession of the nodes. If a solar eclipse occurs at one new moon, which must be close to a node, then at the next full moon the Moon is already more than a day past ...
This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit. [5] The partial solar eclipses on June 12, 2029 and December 5, 2029 occur in the next lunar year eclipse set.
However, targeting in this manner limits the mission designer to changing the plane only along the line of apsides. [citation needed] For Hohmann transfer orbits, the initial orbit and the final orbit are 180 degrees apart. Because the transfer orbital plane has to include the central body, such as the Sun, and the initial and final nodes, this ...