What color is the Moon? The actual color of the Moon is a combination of various shades of gray. We know this from the days of the NASA missions. Photographs, lunar rocks, and soil samples were taken by Apollo Astronauts while on the surface of the Moon.
If gray is its primary color, why do we see so many different colors of the Moon? Why is it called the Blue Moon, Harvest Moon, or the infamous Blood Moon?
This article will explain the answers to all of these questions and more. Read On!
Looking at the surface of the Moon in photographs taken by astronauts in the late 1960s and early 1970s, it is a mixture of magnificent lunar landscapes layered with colors reminiscent of concrete.
The landscape void of life reveals scars from its violent ancient past, leaving countless impact craters and vast dark basins where lava once flowed from lunar volcanic eruptions.
It’s this history, the formation of the Moon, which has provided the palette for its many shades of gray.
How the Moon appears to us has multiple factors which all play a part. Let’s go through each one to understand a little better. First, we’ll begin with why the true color of the Moon happens to be many shades of gray.
Why is the Moon Gray?
The short answer is because of the type of minerals that make up the lunar surface. Minerals like pyroxzene, feldspar, calcium, silicone, iron and magnesium are the basic building blocks of Moon rocks which provide these different shades of gray.
The Moon’s surface, when seen from the sky, is well known for its distinctive areas of white and dark spots, which at times have been visualized as a face in the Moon. These areas are known as the lunar highlands and lowlands.
Lunar Highlands – Terrae
The lighter areas, the lunar highlands named terrae, are primarily made up of a rock called anorthosite.
It is a white plagioclase feldspar, calcium-rich in composition, and represents the very formation of the lunar crust. Samples of this rock, among other types, were brought back on the Apollo missions.
Lunar Lowlands – Mare
The lunar lowlands, darker areas of the Moon, are called lunar mare.
Centuries ago, astronomers thought these were seas hence the name “mare,” or “maria” plural for “seas.”
Maria basins, or flood plains, have a high content of dark volcanic rocks made of basalt created by the rapid cooling of lava rich in iron and magnesium.
Astronomers estimate most of these plains, which covers about 16% of the lunar surface, were created during volcanic activity 3 to 3.5 billion years ago.
These basalts are primarily black but occasionally contain a mineral called olivine. This mineral forms a green crystal when buried at high temperatures and pressures.
However, once exposed to the surface wears quickly and lightens to a greenish hue. As a result, some areas of the Moon have a slight greenish tint.
Titanium is another mineral found within lunar basalt that adds a faint blueish hue across parts of the Moon’s surface.
Craters, Depressions and Soil
Other types of rocks found in craters and depressions are called breccias.
They are formed when impacts on the surface generate high heat, fusing broken fragments of material and creating rocks visibly very similar to a mixture of concrete.
Orange is a color sprinkled on the lunar surface.
An unexpected discovery of orange volcanic glass in the form of beads mixed into the lunar soil was made by Apollo 17 astronauts.
They also found black and green colors of this same type of volcanic glass. The colors of glass correlate to their chemical composition.
Moon rocks break down from constant exposure to harsh elements. The result is called regolith.
It’s the grayish dust/soil we’ve seen the astronauts’ footsteps imprinted on. Since moisture is non-existent on the Moon, it is described as having a loose quality.
The chemical composition of the Moon’s surface is the primary factor producing various shades of light and dark grays as seen from space. But these nuances of green, white, blue, red, and orange from less significant amounts of rocks and minerals still influence its natural color, only in minor brush strokes.
They can be seen more clearly in photographs of the Moon with color saturation, providing more clarity of the undertones of mineral deposits.
Occasionally Earth’s atmosphere will filter the Moonlight, accenting undertones of the lunar surface, making them more visible here on Earth.
This process leads us to the next important factor influencing the appearance of the Moon.
Why Does the Color of the Moon Change?
The Moon’s natural color does not change, but how we perceive it in the sky does. The perception of its color in our eyes is influenced by light viewed through the Earth’s atmosphere.
Atmosphere and Light
The Moon does not produce its own light. Instead, the Moonlight we see is reflective light. It reflects up to 14% of the Sun’s light it receives back into space.
How much light it receives from the Sun depends on its orbital dance around the Earth, creating what is known as the phases of the Moon. A Full Moon will reflect the most light seen here on Earth.
The Harvest Moon is an excellent example of a bright Full Moon. It is the Full Moon appearing closest to the beginning of Autumn and tends to shine longer in the night as seasons enter the autumnal equinox. There is a Full Moon once every month.
The second brightest of the phases is during the phase of Gibbous, which is more than half illuminated, and the least is during a New Moon as its illuminated side faces away from Earth, practically invisible to us. Each phase of the Moon is according to its position in relation to Earth and the Sun, resulting in the Earth’s shadow being visible – or not – on the surface of the Moon.
This white light is then reflected to us here on Earth. However, before this Moonlight reaches our eyes, it must make its way through Earth’s atmosphere, and this is where things can change. Which color of light gets processed by our eyes depends greatly on Earth’s atmospheric conditions.
Our human eyes can only detect wavelengths of light in the visible spectrum. Think of the colors of the rainbow.
We see only a tiny portion, just .0035%, of the much larger electromagnetic spectrum, which includes long waves, infrared, microwaves, x-rays, and gamma rays.
Each color of wavelength has a different size of length measured by the distance from two consecutive peaks or valleys of the light wave. The visible spectrum lies within wavelengths of 380 nanometers (violet) to 750 nanometers (red).
Here on Earth, light waves travel through the atmosphere and air before reaching our eyes.
Rayleigh scattering is a phenomenon that happens during this process. It states the short wavelengths of light, from the bluer end of the spectrum, will be scattered more easily by atmospheric particles unable to reach long distances.
In contrast, the longer wavelengths on the opposite side of the spectrum, such as red, orange, and yellow, will travel much further being affected less.
As a result, the blue light will be dispersed and scattered, unable to be seen from long distances. Red light is less affected by these particles, traveling further and ultimately being perceived as the primary color by the naked eye.
An example of Rayleigh scattering can be observed as the Moon ascends into the night sky. Closer to the horizon, its reflective light has more difficulty reaching our eyes, mainly because it must go through a greater proportion of the atmosphere nearer the Earth’s surface, where it is denser. As a result, it encounters more atmospheric particles like dust, aerosols, and pollution.
These particles equal to or smaller than a wavelength of light can scatter the shorter wavelengths in the spectrum, such as blue and green, preventing us from observing the complete visible range.
With fewer colors visible, the longer wavelengths of light are left as the primary colors reaching our eyes. As a result, the Moon appears to have a reddish-orange glow.
Once the Moon ascends higher in the sky, the atmosphere becomes thinner, scattering fewer wavelengths of the Moon’s reflective light. In turn, more colors get through, and the Moon appears lighter, possibly a shade of yellow, gray, or white.
Occasional Lunar Events
As we discussed earlier, the light of the Moon is reflective. The Moonlight we see ultimately comes from the only light source in our solar system, the Sun.
Much like the Moon, other objects in the sky also reflect light from the Sun, including Earth. Some reflect more and some less, depending on factors like size, composition, angle, and distance from the Sun.
The scientific term used to measure this effect is albedo. Earth’s albedo is approximately .306, meaning around 30%-35% of the light gets scattered back into space. The Moon is around .14 (14%).
Light can also be reflected from one object to another under certain conditions, like the example we will discuss next.
Total Lunar Eclipse – Blood Moon
There are certain lunar events when we know the Moon’s color will be affected. One of the best-known is a total lunar eclipse.
A total eclipse of the Moon happens when the Sun, Earth, and a Full Moon perfectly align. The Earth completely blocks the source of light, the Sun, from reaching the Moon.
As a result, the Moon appears a dim reddish-brown due to the small amount of refracted light it’s now reflecting from the Earth’s atmosphere. As NASA explains, the color is affected by Rayleigh scattering, as most wavelengths of light are scattered away through the filter of Earth’s atmosphere, leaving the longer wavelengths of red, orange and yellow as the primary colors left to be seen in the visible spectrum. It is also referred to as a Blood Moon.
Blue Moon
A very rare event to witness is The Blue Moon when it REALLY is blue.
Most have likely heard the phrase “once in a blue moon” used to reference how scarce or uncommon something is to happen, and rightfully so. Seeing the Moon appear as the color blue is very unusual
but it does happen and can be explained.
The term “Blue Moon” has been used to reference the occurrence of a second Full Moon in one month. It first appeared in the late 19th century, tracking the number of Full Moons through the year for farmers.
Usually, there are three Full Moons in a quarter or season. Still, occasionally there will be a 4th much like the 29th day in February. This 4th Moon in a quarter or season of the year was referenced as a Blue Moon and happens about once every 2.5-2.8 years. Its color does not change and is not the rare Blue Moon that actually appears blue.
According to NASA scientists a Blue Moon will occur when a large number of particles are present in the air or atmosphere a bit bigger than the size of a red wavelength of light (700 nanometers), while no other sizes are present.
The key for this to happen is; The particles must be just the right size, only scattering the longer red light waves. No other sizes are present to scatter the shorter wavelengths of light on the blue end of the visible spectrum. As a result, it allows Blue to pass through as the primary color making the Moon appear… Blue.
Ash and debris blown up into the atmosphere from volcano eruptions or forest fires have been known to create this condition giving the Moon a pale blue color. However, most of the time, the particles are a mixture of sizes preventing this scenario from happening.
Conclusion
The color of the Moon really depends on where it is being observed. In space, it is various shades of lighter and darker gray. From Earth, it can be many colors, as we’ve discussed. Through our eyes, it’s not what color something is but what it appears to be.
Each night brings a new possibility of color to witness.
