Lunar Eclipse

A lunar eclipse occurs when the Earth's shadow falls on the Moon, and a solar eclipse occurs when the Moon's shadow falls on the Earth. A look at the geometry of Moon phases would make it appear that a lunar eclipse should happen at every full moon and a solar eclipse at every new moon. This does not occur because the plane of the Moon's orbit is tilted 5.2° with respect to the plane of the Earth's orbit around the Sun (the ecliptic plane). The conditions for eclipses occur only at the points at which the Moon's orbit passes through the ecliptic plane.

月食发生于地球的影子投落在月球上，而日食发生于月球的影子投落在地球上。观察月相的几何关系会让人以为月食应该发生在每个月的满月时，而日食则发生在每个月的新月时。这并不发生，因为月球轨道平面相对于地球绕太阳公转的黄道平面倾斜了5.2°。只有当月球轨道穿过黄道平面时，才会发生日食和月食的条件。

These illustrations are not to scale and of course greatly exaggerate the 5.2° angle of the Moon's orbit with the ecliptic, but conceptually they show the conditions for eclipses. They were inspired by illustrations in Chaisson and McMillan. The Earth view included is a composite view created by NASA.

这些示意图并非按比例绘制，当然也夸大了月球轨道与黄道面夹角5.2°的实际情况，但概念上它们展示了日食和月食发生的条件。这些插图灵感来源于Chaisson和McMillan的插图。所包含的地球视图是NASA制作的合成图像。

This view of the Moon's orbit helps to explain why you don't get a lunar eclipse every full moon, but only about every six months when the Earth, Moon and Sun line up on the line of nodes.

这种月球轨道的视图有助于解释为什么你不会在每个月满月时都看到月食，而只是大约每六个月当地球、月球和太阳位于交点线上时才会发生月食。