Washington Comprehensive Assessment of Science (WCAS) Practice Test

The phase of the moon that occurs when the entire sunlit side of the moon faces Earth is known as the Full Moon. During this phase, the Earth is positioned between the sun and the moon, allowing the sun's light to illuminate the entire surface of the moon that is visible from Earth. This results in a fully bright moon, often seen as a large, round disk in the night sky.

Understanding the Full Moon phase is essential because it highlights the relationship between the Earth, the moon, and the sun. This alignment leads to the moon appearing completely illuminated, unlike other phases such as the New Moon, where the moon is not visible from Earth, or the Waxing phase, where only part of the moon is illuminated. The Gibbous phase, while it does involve a significant portion of the moon being visible, does not represent the situation where the entire sunlit side is facing Earth. Thus, the Full Moon is the definitive phase representing complete illumination.