If you ask a bunch of people what color is the Moon, you’ll probably get different answers.
Ask your kids and they will say the Moon is yellow. Sometimes, though, it looks more white.
But if you have ever looked at images from NASA’s Apollo mission, then you will probably say the true color of the Moon is gray.
Some may try to sneak in traditional Moon’s phases names such as Blue or Pink Moon.
So, who is right? What color really is the Moon?
What Is The Real Color Of The Moon?
Let me answer you with different questions: what is “real” and what is a color?
Color is a manmade concept: colors do not exist outside our brain.
Colors are the way our brain can distinguish between different electromagnetic radiations within a very narrow range of energy, called the visible spectra.
With electromagnetic radiations (light) within this range, the cells in our retina react and send signals to our brain, which need to find a way to process and make sense of these signals.
In one word, colors.
For example, the color blue is associated with a more energetic electromagnetic radiation than, say, red is.
But not all the colors we see have a physical origin: there are colors, such as pink, that do not exist in the visible spectra. We see them because this is the way our brain interprets a mix of different colors.
So what is the real color of the Moon? As we will see, this will depend on who (or what) is looking and from where.
Why Is Moonlight White?
White, as with pink, is not a color of the visible spectra, but is rather the perceived color for a light source emitting in all the visible colors, like the Sun.
When seen from space, without the “filtering” effect of the atmosphere, the Sun is, in fact white and not yellow.
And since the Moon reflects sunlight back into space, Moonlight is white too.
And the Moon looks white from space.
Cool, we done? That was quick …
Done? No, we just started… go get a cup of coffee and get comfy because you already know that this is not the full story. For us on Earth, the Moon is not always white, right?
Why Does The Moon Sometimes Look A Different Color?
Ask any kid what color the Moon is and he/she will tell you the Moon is yellow.
But have you ever watched the Moon rising or set over the sea from a beach or a boat? That Moon is not white, nor is yellow: it looks dark red!
What Are All Of The Possible Types Of Moon Colors?
The more the Moon climbs in the sky, its color changes from red to orange, to yellow and possibly white, if it climbs high enough in the sky.
You may have now realized by now that this is exactly what the Sun does: it looks red when it is at the horizon during those romantic and awe-inspiring sunsets, but before arriving there, it was orange. And before that it was yellow, and before that it was.. oh well… it was “way too bright to look at”.
After all, the Moon reflects sunlight.
The more atmosphere the Moon and Sunlight has to pass through, the shorter wavelengths are scattered in all directions and only red light reaches us unscattered.
When the Moon and the Sun are high in the sky, their light has to penetrate only a thin layer of atmosphere a few tens of km across at most.
This means the white moonlight and sunlight can reach us almost unaffected.
Ok, so: the Moon looks white from space, and from red to white for us here on Earth, depending on how high the Moon is in the sky. Right?
Right, but wait! There is more: the lunar surface is neither of those colors!
What Color Is The Moon’s Surface?
The Moon’s surface is not really gray, as you may expect if you ever saw NASA’s footage and photos from the Apollo missions and the more recent probes.
Have you ever heard about the Mineral Moon?
At a very large scale, the lunar surface shows subtle colors that depend on the type and relative abundance of the minerals present. Areas rich in iron are reddish, while those rich in titanium are blue.
These shades of colors are too faint to be seen at the naked eye, but we can easily boost them with particular editing techniques of lunar images, mainly image stacking and color saturation.
The higher the Moon is in the sky, the easier it is to make those subtle colors pop, as our atmosphere will not affect Moonlight much.
Okey dokey! So, the Moon looks white from space and gray if you stand on the Moon and look around. For us on Earth, it looks red-orange-yellow-white depending on its altitude in the sky. And on top of that, we can see red and blue patches depending on the lunar surface composition. Gotcha!
Yes, yes, but wait! We have not done yet: have you ever heard about the Blood Moon?
The Blood and Turquoise Moon
Until now, I told you the Moon shines because it reflects sunlight… for the most part. In reality, there is another light source very next to the Moon: Earth!
Earth has a planetary albedo of 0.030 – 0.035: this means that on average it reflects back into space 30-35% of the sunlight it receives.
And this light is strong enough to illuminate the Moon, even if normally the faint Earthshine is easily overpowered by direct sunlight.
But you can easily photograph the earthshine immediately after or right before the new Moon when very little of the Moon is in direct sunlight.
Now, this is very faint light but during a total lunar eclipse, the Earthshine is readily visible on the Moon. And this is not white sunlight and creates interesting colors.
During totality, the Moon looks red, commonly known as Blood Moon.
When this happens, Earth sits in between the Sun and the Moon, shadowing the Moon.
We already saw Earth’s stratosphere (the lower part of the Earth’s atmosphere) scatters and filters out the short-wavelength components of the white sunlight while letting pass the red component more.
When the Moon enters Earth’s shadow (Umbra), the Earthshine illuminates the Moon with a red glow.
But right before totality, with the Moon not yet fully inside Earth’s shadow, another effect becomes visible: the turquoise effect.
Right before totality, a small portion of the redding Moon sits right at the edge of the Umbra, in what is called Penumbra.
Here, the Moon is illuminated by sunlight that passes not through the whole Earth’s atmosphere but just through the thin ozone layer above Earth’s stratosphere.
And because the ozone layer absorbs red light, what reaches the Moon is a nice turquoise color.
I’m very happy I did this article: not only because it is an interesting topic but also, and foremost, because it is a clear demonstration of the intrinsic beauty of the Universe we can explore while trying to answer a seemingly simple and trivial question such as “What is the color of the Moon?”.