Answer: C
Correct answer: Full moon
A lunar eclipse can occur only at full moon, because it requires the Earth to lie between the Sun and the Moon so that its shadow can fall on the lunar surface - and that is precisely the geometry that makes the Moon appear full. By the same reasoning a solar eclipse can occur only at new moon, when the Moon passes between the Sun and the Earth. Eclipses do not happen every month because the Moon’s orbit is tilted about 5° to the plane of the Earth’s orbit, so at most full moons it passes above or below the shadow. Eclipses come only when a full or new moon coincides with the Moon crossing that plane, at points called nodes. A lunar eclipse is visible from the entire night side of the Earth at once and lasts for hours, which is why they are seen far more often from any one place than solar eclipses. The eclipsed Moon usually turns a deep red, because sunlight refracted through the Earth’s atmosphere reaches it after the blue light has been scattered away.