Final answer:
Lunar eclipses do not occur every month because the Moon's orbit is tilted by about 5° relative to the ecliptic path of the Sun. This tilt ensures that the Moon often bypasses the Earth's shadow, except during the eclipse season when its path intersects the ecliptic.
Step-by-step explanation:
Lunar eclipses do not occur every month because the orbit of the Moon is tilted relative to the ecliptic. If the Moon's orbit around the Earth were not tilted by about 5° to the path of the Sun (ecliptic), we would expect a solar and lunar eclipse each month. The tilt causes the Moon to be usually above or below the plane of Earth's orbit and thus avoids the Sun's shadow during most months. Only when the Moon's path intersects the ecliptic, which happens roughly twice a year during the eclipse season, can eclipses occur. A lunar eclipse takes place when the Moon enters the shadow of Earth and is visible from the entire night side of Earth, occurring more frequently than solar eclipses from any given place.