What term describes the progressive changes in the visible portion of the Moon?

The term that describes the progressive changes in the visible portion of the Moon throughout its lunar cycle is known as the phases of the Moon. These phases result from the changing positions of the Moon, Earth, and Sun which cause varying amounts of the Moon's surface to be illuminated as seen from Earth.

This means that at different times during the lunar month, observers on Earth see the Moon in different shapes and sizes, such as new moon, first quarter, full moon, and last quarter, each representing a distinct phase. The concept is fundamental in understanding how lunar illumination works and is key to many astronomical observations and studies.

Eclipses, while also involving the Moon, specifically refer to the events where the Moon passes into the Earth's shadow or the Earth passes into the Moon's shadow, which is a different phenomenon from the phases. Impact craters are depressions formed by the collision of meteoroids with the Moon's surface and do not pertain to the changing appearance of the Moon. Planetshine refers to the light reflected from a planet that illuminates its moon, and it does not describe the Moon's phases either.