What phase occurs when the moon completely passes into Earth's shadow?

The correct answer is the lunar eclipse, which occurs when the moon entirely passes into Earth's shadow. During this event, the Earth is positioned directly between the sun and the moon, causing the Earth to block sunlight from reaching the moon. As a result, the moon takes on a reddish hue due to Rayleigh scattering of sunlight through the Earth's atmosphere, a phenomenon often referred to as a "blood moon." This situation can only happen during the full moon phase when the moon is fully illuminated by the sun and positioned opposite the sun as viewed from Earth.

The other phases, such as the solar eclipse, new moon, and full moon, do not involve the moon entering the Earth's shadow. A solar eclipse occurs when the moon passes between the Earth and the sun, casting a shadow on the Earth. The new moon phase is when the moon is not visible from Earth because it is aligned with the sun. The full moon is simply the phase when the moon is completely illuminated, but it does not involve any shadowing phenomenon.