Question

Why do lunar eclipses not occur on every New and Full Moon day?

Answer 1

Eclipses do not happen on New and Full Moon of every month because, the Moon is above or below the ecliptic plane, i.e., the plane of the Earth's orbit around the Sun. Only when the Moon's orbit crosses through the ecliptic plane, the Sun, Moon and Earth align to produce an eclipse. This occurs at least twice a year, at varying times, for a period of a few weeks.