Editing Eclipse cycle (section)

== Eclipse conditions ==
[[File:Total Solar Eclipse Graphics En 01.svg|thumb|240px|right|A diagram of a [[solar eclipse]] (not to scale)]]

[[Eclipse]]s may occur when [[Earth]] and the [[Moon]] are aligned with the [[Sun]], and the shadow of one body projected by the Sun falls on the other. So at [[new moon]], when the Moon is in [[conjunction (astronomy)|conjunction]] with the Sun, the Moon may pass in front of the Sun as viewed from a narrow region on the surface of Earth and cause a [[solar eclipse]]. At [[full moon]], when the Moon is in [[Astronomical opposition|opposition]] to the Sun, the Moon may pass through the shadow of Earth, and a [[lunar eclipse]] is visible from the night half of Earth. The conjunction and opposition of the Moon together have a special name: [[syzygy (astronomy)|syzygy]] ([[Greek language|Greek]] for "junction"), because of the importance of these [[lunar phase]]s.

An eclipse does not occur at every new or full moon, because the plane of the [[orbit of the Moon|Moon's orbit]] around Earth is tilted with respect to the plane of [[Earth's orbit]] around the Sun (the [[ecliptic]]): so as viewed from Earth, when the Moon appears nearest the Sun (at new moon) or furthest from it (at full moon), the three bodies are usually not exactly on the same line.

This [[orbital inclination|inclination]] is on average about 5°&thinsp;9′, much larger than the apparent ''mean'' diameter of the Sun (32′&thinsp;2″), the Moon as viewed from Earth's surface directly below the Moon (31′&thinsp;37″), and [[Earth's shadow]] at the mean [[lunar distance (astronomy)|lunar distance]] (1°&thinsp;23′).

Therefore, at most new moons, Earth passes too far north or south of the lunar shadow, and at most full moons, the Moon misses Earth's shadow. Also, at most solar eclipses, the apparent angular diameter of the Moon is insufficient to fully occlude the solar disc, unless the Moon is around its [[apsis|perigee]], i.e. nearer Earth and apparently larger than average. In any case, the alignment must be almost perfect to cause an eclipse.

An eclipse can occur only when the Moon is on or near the plane of Earth's orbit, i.e. when its [[ecliptic latitude]] is low. This happens when the Moon is around either of the two [[lunar node|orbital nodes]] on the ecliptic at the time of the [[syzygy (astronomy)|syzygy]]. Of course, to produce an eclipse, the Sun must also be around a node at that time – the same node for a solar eclipse or the opposite node for a lunar eclipse.