What key factor influences the observable phases of the Moon?

The observable phases of the Moon are primarily influenced by the position of the Moon in its orbit around the Earth. As the Moon travels along its elliptical path, different portions of its surface are illuminated by the Sun. This changing illumination creates the various phases we see from Earth, which include the New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent.

The Moon's position determines how much of its illuminated side faces Earth at any given time; hence, it is the relative positions of the Earth, Moon, and Sun that create the observable phases. For instance, during a New Moon, the Moon is positioned between the Earth and the Sun, with the illuminated side facing away from Earth, making it nearly invisible to us. Conversely, when the Moon is on the opposite side of the Earth from the Sun, we see a Full Moon, as the entire illuminated side is facing us.

By contrast, factors such as the Moon's distance from Earth, the brightness of the Sun, and the Earth's rotation do not directly create the phases of the Moon. While the distance can affect the size and appearance of the Moon from Earth, it is not a primary cause