An eclipse is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the shadow of Earth.

    Eclipses may occur when the Earth and Moon are aligned with the Sun, and the shadow of one body cast by the Sun falls on the other. So at New Moon (or rather Dark Moon), when the Moon is in conjunction with the Sun, the Moon may pass in front of the Sun as seen from a narrow region on the surface of the Earth and cause a solar eclipse.

    At Full Moon, when the Moon is in opposition to the Sun, the Moon may pass through the shadow of the Earth, and a lunar eclipse is visible from the night half of the Earth.

    An eclipse does not happen at every New or Full Moon, because the plane of the orbit of the Moon around the Earth is tilted with respect to the plane of the orbit of the Earth around the Sun, so as seen from the Earth, when the Moon is nearest to the Sun (New Moon) or at largest distance (Full Moon), the three bodies usually are not exactly on the same line.

When does lunar eclipse happen?