Short answer
A waxing moon shows an increasing illuminated portion to observers on Earth; a waning moon shows a decreasing portion. Waxing runs from new toward full, while waning runs from full toward new. These labels concern the visible disk, not how much of the whole Moon receives sunlight. 1 2
On this page
At a glance
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| Question or attribute | Waxing moon | Waning moon |
|---|---|---|
| What changes? | Visible illuminated portion increases | Visible illuminated portion decreases |
| Where in the cycle? | New toward full | Full toward new |
| Named appearances | Waxing crescent, first quarter, waxing gibbous | Waning gibbous, third quarter, waning crescent |
| Does the Moon produce the light? | No; it reflects sunlight | No; it reflects sunlight |
The phase sequence supplies the comparison; sunlight supplies both appearances. 1 2
What each thing is
Neither term names a separate object or one fixed silhouette. Each groups a progression of appearances: waxing includes both crescent and gibbous phases, and waning includes those same shape categories in reverse order. Crescent versus gibbous is therefore a different distinction from waxing versus waning. 1
Key differences
The defining contrast is direction, not simply how much illumination is visible at one moment. In the listed cycle, first quarter belongs to the progression toward full; third quarter belongs to the progression toward new. NASA explicitly describes third quarter as a half-illuminated apparent disk whose illuminated fraction is decreasing. 1
How to tell them apart
Compare the visible illuminated portion across successive nights: an increase indicates waxing, and a decrease indicates waning. The limit is that one isolated shape may not establish the direction of change. Location also matters to observing conditions; these excerpts do not establish a hemisphere-specific left/right identification rule. 1 2
Where they overlap
Both are views of the same Moon reflecting the same Sun’s light. The Moon remains half-lit even though different amounts of its illuminated surface are visible from Earth. Both also belong to one repeating phase cycle, which takes about 29.5 days from new moon to new moon. 1 2
Edge cases
New and full moon mark the boundaries between the two progressions. NASA lists them as separate phase names rather than calling them waxing or waning. Near those boundaries, identifying the adjacent direction requires knowing whether the visible illuminated portion is increasing or decreasing—not merely recognizing a nearly dark or nearly full disk. 1
Why the distinction exists
The terminology separates a changing Earth-based appearance from the Moon’s physical illumination. Saying that the Moon is waxing does not mean sunlight is reaching an ever-larger fraction of the whole lunar surface: the sources describe one half as illuminated. It means the illuminated portion presented to Earth is increasing. 1 2
Common misconceptions
Waxing does not mean “crescent,” and waning does not mean “almost dark”: both progressions contain crescent and gibbous phases. Nor is nighttime visibility the definition. NASA notes that the Moon can be visible during daylight and that viewing times depend on phase, season, and location. 1 2
Examples
Hypothetical case 1: a crescent’s illuminated portion grows over successive nights toward first quarter. That is waxing, even while the Moon still looks narrow. Hypothetical case 2: a broad illuminated disk shrinks after full moon toward third quarter. That is waning, even while much of the disk remains illuminated. Both cases apply NASA’s phase sequence. 1