The 'Moon illusion' has been baffling scientists for thousands of years

It's an illusion that has left everyone from the worlds of philosophy and science perplexed for thousands of years - but why does the Moon seemingly appear larger when it's rising or setting?

Questions over the optical trickery of the moon's larger appearance near the horizon can date back to the 4th century BCE.

That's right, even Aristotle scratched his chin to ponder what exactly causes this. The best he came up with was that the Earth's atmosphere had magnifying properties to distort what the moon looks like.

At the horizon point, where the moon illusion is clear to see, the philosopher reckoned light has to pass through more of the dense atmosphere and results in a magnifying glass effect.

With this theory, it is clear Aristotle understood how the moon illusion tricks the human eye rather than it being caused by the moon or space - though not all of his theories were as astute.

This is a trick to the human eye because when you get a photograph of the moon and record its measurements, each night it stays the same size - no matter what it looks like to us in the night sky.

The Moon Illusion has sparked plenty of theories and debates over the yearsiStockphoto by Getty Images

So we've all accepted that it is an optical illusion, and nowadays the reason suggested for this is down to our brains not being able to comprehend the size and distance of the Moon.

However, there is no clear-cut answer as to why - a possible reason could be the surroundings which impact our perceptions - e.g. trees, mountains, and buildings that make us think the moon is closer and larger than it actually is when it's on the horizon.

When the moon is high up in the sky with nothing surrounding it to as a size reference, then this makes it appear further away and smaller.

Sound familiar? That would be because the Ponzo illusion is similar in this regard since the pair of converging lines distorts the perception of two identically sized lines.

So while we may think the upper line is larger and farther away, this is not the case - both lines are the same size.

When in doubt, let's see what NASA have to say about this moon illusion.

“In the absence of a complete explanation for why we see it like that, we can still agree that – real or illusion – a giant Moon is a beautiful sight," the space agency said, as per IFL Science.

“So, until someone puzzles out exactly what our brains are up to, it's probably best to just enjoy the Moon illusion, and the moody, atmospheric, and sometimes downright haunting vistas it creates."

Something to think about next time you find yourself gazing up at the moon...

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