Do you see craters or bumps on the Moon’s surface?

Optical illusion on moon: Craters or bumps? Photo / iSpace via The New York Times

A picture of the Moon’s south pole was taken in May by Resilience, a robotic lander operated by the Japanese company Ispace that probably crashed on the lunar surface last week. Some people see bumps, but others see craters.

What you’re seeing is known as the crater illusion, or sometimes relief inversion. In this illusion, features of a landscape appear to reverse their elevation. It occurs because our brains have limited information about the source and the direction of light in an image.

Susana Martinez-Conde, a neuroscientist at SUNY Downstate Health Sciences University in Brooklyn, says our brains tend to assume that light comes from above. That’s because we live on Earth, under the sun.

But in space, the direction of illumination can be more complicated to figure out. Light may fall on a surface horizontally, or even be cast from below.

In the lunar landscape photographed by the Ispace Resilience spacecraft, light appears to be coming from below, which to some gives the appearance of a bumpy Moon. Flipping the image, so the light comes from above, may have allowed your brain to compensate and see craters instead.

The dress that broke the internet after a BuzzFeed post in 2015 is one of the most famous examples of an illusion arising from ambiguous lighting.

Other craterlike illusions abound for similar reasons. There are paper plates that may look upside down when they are really resting on their bottoms. Images of footprints in the sand can appear raised, rather than hollow.

And then there are buttons that seem concave or convex, depending on the orientation.

The same effect is sometimes produced by Nasa satellites capturing images of craters on Earth from above.

“Illusion is by definition a discrepancy, a mismatch between objective reality and our subjective perception of that reality,” said Martinez-Conde, who organises a worldwide contest for best illusion of the year.

In person, your brain has a better sense of depth, of the way shapes change as you move around and of how shadows fall, all of which can help it interpret where the light is coming from.

But the brain is more easily tricked with photographs because of the limited information pictures can have.

One reason you may see bumps where there are craters in the lunar south pole image is that the depiction of the Moon lacks a clear light source. Nor is there any other object for your brain to compare shadows, size or depth with.

If you can see only bumps – or craters, for that matter – Martinez-Conde suggests tilting your head, switching your gaze from one place to another or just staring at the image for a while. Flipping it can also help.

Martinez-Conde saw craters when she first saw the image. But now her brain is perceiving bumps after using these tricks.

She even printed out a copy of the image. The bumps endure. So much for objective reality.

But there may be value in switching perceptions. Neuroscientists study optical illusions to help them understand the mechanisms our brains use to construct our experience of reality. Optical illusions also encourage critical thinking skills, Martinez-Conde said, because they show us that there can sometimes be a disconnect between what is real and what we perceive.

“I know that my perception is incorrect, but there’s nothing I can do to flip it,” she said of the lunar image. “Just because you feel that something seems to be true, and that it’s hard for you to consider the opposite perspective, doesn’t mean that you’re necessarily correct.”

This article originally appeared in The New York Times.

Written by: Katrina Miller

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