During which of the following phases can a lunar eclipse occur?

A lunar eclipse occurs only when Earth passes between the Sun and the Moon so that Earth's shadow falls on the Moon. Because the Moon's orbit is tilted about 5 degrees to Earth's orbital plane, this alignment is possible only at Full Moon (opposition), and only when the Moon is additionally near a lunar node at that time -- so Full Moon is a necessary condition for a lunar eclipse, though not every Full Moon produces one.

Among the four moon phases listed, Full Moon is the only phase where the Sun-Earth-Moon opposition needed for a lunar eclipse can occur at all -- New Moon and the two quadratures rule it out on their own geometry, as explained below. So among these options, Full Moon is the phase during which a lunar eclipse can occur.

• New Moon: here the Moon sits between the Sun and Earth (conjunction), the opposite alignment -- this geometry can only produce a solar eclipse, never a lunar one.

• First Quadrature: the Sun-Earth-Moon angle is close to 90 degrees, so the Moon is off the Sun-Earth line and no shadow can fall on it -- no eclipse is possible at this phase.

• Third Quadrature: the angle is again close to 90 degrees, on the opposite side of the orbit, so the same reasoning rules out an eclipse here too.

Only the Full Moon phase satisfies the necessary opposition geometry for a lunar eclipse; the other three phases geometrically rule an eclipse out entirely.