[MUSIC]
What color is the moon?
I asked you all this question and got some very interesting answers.
Silver like aluminum
white, like the color of clouds
Chalky, like ash
silver, kind of like an old coin
gray like pavement
silver like your mother's hair
milky chalk
gray like a used eraser
white, like a diamond
But among all the varied responses and interesting comparisons, you all pretty much agreed: The
moon is a very light color, something like this.
But what if i told you it was actually more like this
[MUSIC]
When our brains are trying to figure out what color something is
the first thing we do is try to figure out how bright it is.
This side of the apple looks like a brighter color than
the side away from the light, we can see that is so,
but our brains are able to take this lighting into
account and we know that the whole apple is the same red.
If a car drives out of a dark tunnel, we don’t assume the car magically
changed color, because our brains correct for differences in all the light
in whatever scene we’re looking at.
But that doesn't always work so well.
Here's a white square
No, here's a white square.
No, here's a white square
Wait a second, what is going on here?
All these squares are the same.
And you may have seen this famous illusion before. The two lettered squares are actually the
same color.
Even when the light in a scene doesn’t change, the colors surrounding an object can also
trick our brains. If you stare at the center of this image, between the yellow and blue
bars, the tiny squares look like different colors, but they’re not.
If our brains could make an absolute measurement of light passing through our pupils, maybe
we wouldn’t be tricked by these illusions. But we can’t do that, our eyes aren’t cameras
or light meters or that little eyedropper tool in Photoshop.
As far as our brains are concerned, it’s not what color something is, it’s what
color something appears to be.
Which brings us back to the moon. The full moon gives enough light that
it can even cast shadows on the ground on a dark night here on Earth. But it only looks so blindingly
bright in the night sky because there’s nothing else nearby it to compare to, except
the night sky itself.
Instead of measuring the absolute
number and wavelength of photons the moon gives off, our eyes and brains compare the relative amounts
of light given off by two or more objects within our field of view.
Consider these shapes. The smaller rectangles in the center are the same color, but since
the *relative* difference between the two top shapes is greater, the small rectangle
*appears* brighter up top.
The lightest object in a scene becomes a sort of anchor, our brains say “that’s white”,
So how bright is the moon?
Not that bright. The moon only reflects about 13% of the light that hits its surface. But
in the night sky, against the dark blackness of space, it’s the brightest
thing we can see, so our brains tell us “that’s white”.
But if we viewed the moon next to Earth, under the same illumination, it would be a very
dark gray, almost like an asphalt road. In fact, you can see this dark gray color in
photos taken on the Moon during the Apollo missions. Compared to a white spacesuit, suddenly
the moon doesn’t seem as bright, does it?
I hope you’ve enjoyed this little mind-bender, and that next time you look up at the moon,
you don’t see it in exactly the same light.
Remember, the eye and mind work together in mysterious ways, and…
“Colours, seen by candle-light Will not look the same by day.”
Stay curious.