Why do solar eclipses happen only at certain times?

Solar eclipses do not happen every new moon because the Moon’s orbit is tilted relative to Earth’s orbit around the Sun. Most months, the Moon passes slightly above or below the line between Earth and the Sun. Only when a new moon occurs near one of the Moon’s orbital nodes does the shadow fall on Earth. Total solar eclipses are especially brief because the Moon’s shadow path is narrow, often only about 100 to 200 kilometers wide. Predictions of eclipses were a major early success of celestial mechanics and are now calculated centuries in advance.