<P> An eclipse cycle takes place when eclipses in a series are separated by a certain interval of time . This happens when the orbital motions of the bodies form repeating harmonic patterns . A particular instance is the saros, which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years . Because this is not a whole number of days, successive eclipses will be visible from different parts of the world . </P> <P> An eclipse involving the Sun, Earth, and Moon can occur only when they are nearly in a straight line, allowing one to be hidden behind another, viewed from the third . Because the orbital plane of the Moon is tilted with respect to the orbital plane of the Earth (the ecliptic), eclipses can occur only when the Moon is close to the intersection of these two planes (the nodes). The Sun, Earth and nodes are aligned twice a year (during an eclipse season), and eclipses can occur during a period of about two months around these times . There can be from four to seven eclipses in a calendar year, which repeat according to various eclipse cycles, such as a saros . </P> <P> Between 1901 and 2100 there are the maximum of seven eclipses in: </P> <Ul> <Li> four (penumbral) lunar and three solar eclipses: 1908, 2038 . </Li> <Li> four solar and three lunar eclipses: 1918, 1973, 2094 . </Li> <Li> five solar and two lunar eclipses: 1934 . </Li> </Ul>

In a solar or lunar eclipse the region of earth's shadow is divided into