The Moon’s appearance often shifts in color, from brilliant white to shades of yellow, orange, and red. This variability raises a fundamental question: what is its true color, and what factors contribute to its changing perceived appearance? Understanding these phenomena involves exploring the Moon’s surface composition, light reflection, and how our eyes and Earth’s atmosphere interact with incoming light.
The Moon’s Actual Color
The Moon’s inherent color is not white, but a dark gray, similar to asphalt. Its surface is predominantly shades of gray, with occasional hints of tan and brown. This color stems from its composition: dark volcanic rocks like basalt, and a fine, powdery layer called regolith. Lunar regolith, formed from billions of years of meteoric impacts, consists of pulverized rock and mineral fragments, including feldspar, pyroxene, and olivine. The Moon reflects sunlight, but its surface materials absorb most incoming light, reflecting only 3% to 12%.
Why It Appears White
When the Moon is high in the night sky, its brightness against the dark backdrop of space often makes it appear white or silvery. Our eyes’ light receptors, particularly rod cells, are highly sensitive to bright objects in dim surroundings. This can lead to saturation, causing us to perceive white as all wavelengths of light are processed equally. Earth’s atmosphere also plays a role; when the Moon is high overhead, its light travels through a thinner section of the atmosphere. The sheer brightness of the reflected sunlight dominates, leading to a perceived white color.
Other Perceived Colors of the Moon
The Moon frequently appears in colors beyond white or gray, often exhibiting yellow, orange, or red hues, especially near the horizon during moonrise or moonset. This variation is primarily due to atmospheric scattering, where particles in Earth’s atmosphere interact with light. As moonlight travels through more atmosphere at lower angles, shorter wavelengths like blue and green are scattered away by dust, pollution, and water vapor. This allows longer wavelengths, specifically red, orange, and yellow, to reach our eyes more directly. Factors like dust from wildfires or volcanic ash can intensify these effects, causing a deeper red or orange appearance, as seen during a total lunar eclipse when sunlight is filtered through Earth’s atmosphere, bending red light onto the lunar surface.