.- LA LUNA LUNAR ORBIT.
For observers, before embarking on an observation of the Moon, should know its orbit around the Earth, to understand its apparent movement and the various issues that may occur in the sky to an observer on Earth.
The Moon is the astronomical object closest to the Earth. The moon rotates
long around the Earth describing an ellipse in one of whose foci is the Earth with a large tilt igual a 0,05490. Siguiendo este valor, el perigeo (distancia mínima de la Luna a la Tierra) está en 363.296 Km. y el apogeo está en 405.50, siendo la distancia media 384.400 Km. Su semieje mayor es de 384.399,1 Km, la inclinación respecto de la eclíptica es 5,14540 (fracción de grado) o 5º 08´ 43 ,33017´´ (grados sexagesimales). La longitud del nodo ascendente y la latitud del perigeo varían cíclicamente con el tiempo entre 0º y 360º, y no se les puede definir con un valor medio.
La intersección de la órbita lunar y la eclíptica determinan una recta que corta en dos puntos, denominados nodo ascendente y nodo descendente. Sólo en los puntos del nodo ascendente and down results in the phenomenon of eclipses, both lunar and solar. The line connecting two nodes is called line of nodes. This line does not conseva a fixed direction with respect to distant stars, but retrograde in reverse on the plane of the ecliptic the moon's orbital motion with a period of 18.6 years (6793.5 days). As a result, to return to the same node, you must perform at least one complete revolution (month draconícito).
The line joining the perigee and apogee is called the apsidal line. This line has a direct movement and takes place in the lunar orbit plane. Its period is 8.85 years (3232.6 days).
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