The terms “waxing” and “waning” are ancient descriptors used to define change, specifically the direction of growth or shrinkage. Originating in Old English, they convey a simple concept: something is either getting bigger or getting smaller. While most commonly associated with the cycles of the Moon, their literal meanings apply broadly to any phenomenon that exhibits a measurable rise or fall.
The Core Meaning of Waxing and Waning
The verb “wax” is rooted in the Old English word weaxan, which translates to “to grow” or “to increase.” “Waxing” signifies a period of expansion or augmentation. Conversely, “wane” implies a reduction in size, strength, or intensity, meaning “to diminish” or “to fade away.” These two terms function as perfect directional opposites, establishing a clear binary state of change.
This directional clarity allows the words to be used beyond astronomy to describe various non-astronomical trends. For instance, a politician’s influence might be described as “waxing” if their popularity is increasing. Conversely, public interest in a news story is “waning” if it begins to fade.
How the Terms Apply to Lunar Visibility
When applied to the Moon, “waxing” and “waning” describe the changing fraction of the sunlit face visible from Earth as the Moon orbits our planet. The waxing phase begins immediately after the New Moon, when the Moon is not visible because its sunlit side faces away from Earth. As the Moon moves toward the Full Moon position, the sliver of illuminated surface we observe steadily grows larger, transitioning through the Waxing Crescent and Waxing Quarter phases.
The waxing cycle culminates at the Full Moon, where the entire visible hemisphere is illuminated by the Sun. This change in visibility is not a physical change in the Moon itself, but a result of the shifting angle between the Earth, Moon, and Sun.
Following the Full Moon, the Moon enters its waning cycle, where the illuminated area visible from Earth begins to shrink. During this half of the lunar cycle, the Moon travels back toward the New Moon position, passing through the Waning Gibbous and the Waning Quarter phases.
The process of waning continues until the Moon reaches the New Moon phase again, completing its approximately 29.5-day synodic cycle. This constant orbital motion ensures the Moon is perpetually engaged in either a waxing or a waning state.
Simple Visual Cues for Identification
Identifying whether the Moon is waxing or waning can be simplified by observing which edge of the disk is illuminated, particularly in the Northern Hemisphere. During the waxing phases, the illuminated portion always appears on the right side of the Moon and expands toward the left. Conversely, when the Moon is waning, the illuminated portion is seen on the left side of the disk and shrinks toward the right.
A common visual trick is to recognize that a waxing gibbous Moon resembles the shape of the letter ‘D’ and a waning crescent Moon resembles the letter ‘C’. This visual identification provides an immediate cue for the direction of change in the lunar cycle.
It is important to note that this right-side/left-side rule is reversed for observers in the Southern Hemisphere due to their different viewing perspective. However, the underlying principle of increasing or decreasing illumination remains consistent globally.
Usage in Other Contexts
The concepts of waxing and waning extend far beyond the celestial sphere, providing powerful metaphors in literature and language. Any measurable phenomenon that exhibits a directional change can be described using these terms, including non-physical concepts like emotional states. For instance, one’s confidence might be waxing after a success or waning after a setback.
In scientific fields other than astronomy, the terms describe measurable fluctuations in intensity. A beam of light might be described as waxing in brightness as a power source is increased, or a sound wave could be described as waning in amplitude as it travels away from its source. In all applications, the words maintain their original function: clearly indicating a direction of positive or negative change.