6.16 Eclipses and the Moon's orbital inclination

Eclipses don't occur at every new and full moon because the Moon's orbit is tilted slightly with respect to the Earth's orbit around the Sun. As a result, at the time of month when the Moon lies toward the Sun, it may be below or above the Earth' s orbit and its shadow cannot fall on the Earth, nor can the Earth's shadow fall on the Moon. However, because the Moon's orbit keeps approximately the same tilt, a time will come twice each year when the Earth, Moon, and Sun line up so that eclipses will occur.