Many people imagine the Moon as a bright white or yellow orb, sometimes appearing orange. This perception does not reflect the Moon’s actual color. The variations in how we see the Moon are largely due to atmospheric effects and its diverse geological features.
The Moon’s True Appearance
In the vacuum of space, the Moon primarily exhibits dull shades of gray and brown. This coloration stems from its surface material, regolith, a layer of pulverized rock, dust, and fragments. The lunar regolith is rich in minerals such as oxygen, silicon, magnesium, iron, calcium, and aluminum. The overall gray appearance is comparable to charcoal or asphalt.
While predominantly gray, the Moon also displays subtle hints of other colors, including very dark reds, blues, and greens, depending on the specific mineral content of different regions. These slight color variations are often difficult to discern with the unaided eye but become apparent in highly saturated images taken by spacecraft.
How Earth’s Atmosphere Influences Perception
Earth’s atmosphere significantly alters our perception of the Moon’s color, causing it to appear in hues from white to yellow, orange, or red. This phenomenon is due to Rayleigh scattering, which explains why the sky appears blue. As moonlight, reflected sunlight, passes through Earth’s atmosphere, shorter blue and violet wavelengths are scattered more effectively by atmospheric particles. This scattering allows longer wavelengths, such as red and orange light, to pass through more directly.
When the Moon is low on the horizon, its light travels through a greater thickness of the atmosphere, leading to more scattering of blue light and a more pronounced reddish or orange appearance. Dust, smoke, and pollution can further intensify these color effects. For example, during a total lunar eclipse, the Moon can turn a deep red because sunlight is filtered and bent by Earth’s atmosphere, projecting only the red and orange light onto the lunar surface.
Variations on the Lunar Surface
Beyond atmospheric effects, the Moon’s surface exhibits subtle color variations due to its diverse geological makeup. The lunar surface is divided into two main types of terrain: the darker, smoother plains known as “maria” (Latin for “seas”) and the lighter, heavily cratered “highlands.” These regions reflect light differently because they are composed of distinct materials.
The maria are vast, dark basaltic plains formed by ancient volcanic eruptions that filled large impact basins. These basaltic rocks are rich in iron and appear darker because they are less reflective. In contrast, the lunar highlands are primarily composed of anorthosite, a lighter-colored rock rich in aluminum and calcium. This material reflects more sunlight, making the highlands appear brighter. These compositional differences contribute to the Moon’s nuanced appearance, revealing a complex geological history.