The Sun's (S) shadow cones ( umbras ) of the Moon (M) and the Earth (E) are revolving, relatively.. When the Moon's umbra sweeps the Earth's surface, it is solar eclipse. If the Earth's shadow sweeps the surface of the Moon, it is lunar eclipse. These do not happen in every New Moon and Full Moon. They happen, when the ∠ E M S , during New Moon, and the ∠ M E S . during Full Moon, are very near 180 o , for near-perfect alignment.
