A syzygy (pronounced SIZ-uh-jee) is the alignment of three celestial bodies in a straight line. Most commonly, astronomers use it to describe when the Earth, Moon, and Sun line up, which happens during every full moon and new moon.

During a solar eclipse, the Moon passes directly between Earth and the Sun, creating a syzygy that blocks the Sun's light. During a lunar eclipse, Earth moves directly between the Sun and Moon, casting its shadow on the Moon. Both eclipses require this three-body alignment.

Scientists also use it to describe alignments of other planets, like when Jupiter, Saturn, and the Sun form a straight line.

You might encounter syzygy in science class when studying astronomy, or in word games where it's valued for being one of the few English words without the traditional vowels A, E, I, O, or U.