The term “White Moon” is not a formally recognized designation within astronomy, unlike established phases such as the full moon or new moon. This popular phrase refers both to a visual phenomenon—the brilliant, silvery appearance of the Moon when high in the night sky—and to traditional, non-scientific concepts. The perceived color is a complex interplay between the Moon’s inherent physical properties and the distorting influence of Earth’s atmosphere. Understanding the “White Moon” idea requires distinguishing between the Moon’s actual shade and its visual presentation.
The Moon’s True Color and Reflectivity
The Moon itself is not inherently white but possesses a surprisingly dark surface, closer in color to old asphalt or charcoal gray. Its surface is composed primarily of regolith, a fine, powdery material created by continuous meteorite impacts on volcanic rock. The overall reflectivity of the Moon’s surface, known as its albedo, is very low, reflecting only about 7% to 12% of the sunlight that strikes it.
If viewed outside Earth’s atmosphere, the Moon’s true appearance would be a dull, dark gray orb against the blackness of space. The perception of it being a bright, white object is entirely due to the contrast between its sunlit surface and the dark night sky. Although the amount of light reflected is small, the absence of other bright objects allows that light to dominate our field of vision, making it appear brilliant.
The presence of dark, solidified lava flows, which form the large, smooth plains known as maria, further lowers the average albedo of the near side. Conversely, the brighter, heavily cratered highland regions are composed of more reflective rock types. This difference in composition creates the light and dark patterns visible from Earth.
How Earth’s Atmosphere Affects the Moon’s Appearance
The primary reason the Moon appears white or silvery-white when seen high overhead is the way Earth’s atmosphere interacts with light. The atmosphere acts as a selective filter, causing the perceived color of any celestial object to change depending on its altitude above the horizon. The light reflected from the Moon, which is essentially white sunlight, must pass through this atmospheric layer before reaching our eyes.
When the Moon is high in the sky, its light travels through the least amount of atmosphere, resulting in minimal interference. This allows the full spectrum of reflected light to reach the viewer, making the Moon appear at its brightest and closest to a neutral white or silvery hue. This high-altitude appearance is the closest view we get without atmospheric distortion.
The phenomenon of Rayleigh scattering explains the changes in lunar color as the Moon rises or sets. Air molecules and tiny particles scatter shorter wavelengths of light, such as blue and violet, much more effectively than longer wavelengths like red and orange. When the Moon is near the horizon, its light must pass through a significantly thicker layer of air, scattering almost all of the blue light away from our line of sight.
Only the longer, less-scattered wavelengths—the reds and oranges—are left to travel directly to the observer, which is why the Moon can look deep yellow, orange, or even red when it is low. As the Moon climbs higher, the path length through the atmosphere shortens, less light is scattered, and the full spectrum is preserved, returning the Moon to its typical bright white appearance.
“White Moon” in Cultural and Calendar Systems
Outside of the scientific explanation for its bright appearance, the term “White Moon” holds symbolic meaning in various cultural and spiritual contexts. In some traditions, particularly within neopaganism, the concept of a “White Moon cycle” is applied to the human menstrual cycle. This refers to the pattern where menstruation aligns with the New Moon, and ovulation occurs around the Full Moon.
This alignment is associated with the energies of creation, fertility, and nurturing, reflecting a focus on inner healing and domesticity. The visually dark New Moon is considered a time for drawing inward, corresponding to the restorative phase of menstruation. Conversely, the light of the Full Moon symbolizes the outward-facing, fertile peak of the cycle.
In other historical or religious contexts, the term carries connotations of purity or illumination. In Jainism, the “White Moon” is a symbol seen in the auspicious dreams of Trishala, representing elegance and purity. Additionally, the Arabic term for full moon, badr, sometimes translates to “white moon” and refers to Al-Ayyam Al-Beed, or “The White Days,” surrounding the full moon.
These non-astronomical uses demonstrate that the “White Moon” is a concept rooted in symbolism and tradition rather than a technical lunar phase. It denotes a period of time or a spiritual state associated with cleansing, brightness, or a specific energetic alignment.