sentences:  Eclipses occur when the three bodies form a nearly straight line.Because the plane of the lunar orbit is inclined to that of the Earth, this condition occurs only when a full or new Moon is near or in the ecliptic plane, that is when the Moon is at one of the two nodes (the ascending or descending node).The period of time for two successive lunar passes through the ecliptic plane (returning to the same node) is termed the "draconic month", a 27.21222 day period.