A full moon is a beautiful sight that has captivated humans since the beginning of time. When the moon is full, it appears as a bright, round disc in the night sky. But is this striking orb glowing white or yellow? The answer lies in an understanding of the moon’s phases and how sunlight interacts with the lunar surface.
What Causes the Phases of the Moon?
The moon orbits around the Earth in an elliptical path once every 27.3 days. As the moon circles our planet, its position relative to the Earth and sun changes. This causes the moon to go through phases from new moon to full moon and back again.
| Moon Phase | How Much of the Moon’s Disk is Illuminated |
|---|---|
| New Moon | 0% |
| Waxing Crescent | 1% to 49% |
| First Quarter | 50% |
| Waxing Gibbous | 51% to 99% |
| Full Moon | 100% |
| Waning Gibbous | 51% to 99% |
| Last Quarter | 50% |
| Waning Crescent | 1% to 49% |
During a full moon, the moon is on the opposite side of the Earth from the sun. So the side of the moon that faces us is fully illuminated by sunlight. This results in the entire visible disk of the moon appearing bright and round in our sky.
The Color of Moonlight
When sunlight hits the moon’s surface, the light is reflected back out into space. The color we perceive this reflected light to be depends on the composition of the material on the moon’s surface.
The lunar surface is made up of dark gray to black basaltic plains and lighter powdery soil called regolith. It also contains small amounts of iron-rich minerals like pyroxene and olivine. The regolith has a somewhat yellowish tint to it.
But the moon’s surface reflects only about 12% of the sunlight that strikes it. The reflected light appears white to our eyes because it is a combination of all wavelengths of visible light mixed together. Just like white light from the sun appears white to us rather than yellow.
However, during a full moon, there can be a very slight yellow or orange glow. The moon’s light often looks more yellow or orange when it is close to the horizon. This is due to the scattering of more blue light by Earth’s atmosphere at low angles, allowing more red and yellow hues to pass through.
Does the Moon Look Different Colors Other Than Full?
When the moon is not full, it appears darker with varying amounts of illumination. During phases like the crescent moon, the moon can take on a yellowish or orange hue even when high in the night sky.
Without the bright white full phase to wash out the light, the moon’s natural yellowish color reflected from the regolith material on its surface becomes more apparent. In addition, during partial phases the moon’s light has to travel through more of Earth’s atmosphere which filters out blues and gives a yellow tint.
| Moon Phase | Typical Color |
|---|---|
| Full Moon | White |
| Gibbous | White to pale yellow |
| Quarter | Pale yellow |
| Crescent | Yellow to orange |
Does Color Vary for Supermoons and Minimoons?
The moon’s perceived color can also change slightly depending on if it is at perigee or apogee in its elliptical orbit.
Perigee is when the full moon is at its closest orbital point to Earth, making it appear up to 14% larger and 30% brighter than an average full moon. This “supermoon” effect enhances the moon’s white glow.
In contrast, when the full moon is at apogee or the most distant point in its orbit, it can appear up to 14% smaller and somewhat dimmer. This “minimoon” may have more of a subdued yellowish hue.
| Moon Event | Distance from Earth | Appearance |
|---|---|---|
| Perigee “Supermoon” | 225,300 miles | Large, bright white disk |
| Apogee “Minimoon” | 252,600 miles | Small, somewhat dimmer with yellowish hue |
However, the difference in apparent size and brightness between a supermoon and minimoon is quite subtle to the naked eye.
Conclusion
The full moon is most accurately described as white in color when viewed high in the night sky. This is because it reflects sunlight back to Earth which contains all visible wavelengths of light.
However, the moon can take on a yellow, orange, or golden hue during partial phases or when close to the horizon due to the scattering of blue light in Earth’s atmosphere. The moon’s regolith surface also gives a slightly yellow tint to the reflected light that is more apparent when the moon is not full.
While the moon may appear ever so slightly yellower when smaller in its apogee phase, the difference is not overly noticeable without looking through a telescope. The exception is during a Blood Moon total lunar eclipse when the moon actually takes on a reddish hue.
So in summary, the moon is neither purely white nor yellow. Its apparent color is variable depending on lighting and viewing conditions. But our bright full moon will most often shine white against the celestial backdrop of space.
