A stunning supermoon is set behind the Kremlin in Moscow, Russia as appearing larger due to the Moon illusion effect (Photo: Reuters)
If you looked up at the sky and thought the Moon looked unusually large and bright recently, you weren't imagining it entirely but you were being fooled a little. What you witnessed was a combination of two fascinating event as a supermoon and something known as the Moon illusion. While the Moon did reach its closest point to Earth, the perception that it suddenly swelled in size or hovered nearer is mostly a clever trick of the human mind.
A supermoon occurs when the Moon reaches perigee the closest point to Earth in its elliptical orbit at the same time it becomes full. In this alignment, the Moon can appear up to 7% larger and 15-30% brighter than usual.
These differences are measurable but are actually far subtler than we perceive. The apparently gigantic Moon dominating the horizon during a supermoon owes much of its drama to our brains rather than its true physical position.
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Although the Moon's size does not actually appear to change whether it is high in the sky or hovering low near the horizon, this really is an illusion. When we see the Moon with familiar objects such as trees, buildings and hills our brain interprets it as being farther away, and so it looks larger.
Since the actual image of the Moon on our retina is not larger, our brain simply compensates to make sense of this apparent distance by making the object appear larger. A similar illusion can be seen in the Ponzo illusion, in which converging lines are used to trick the mind into believing equal-sized objects differ in scale.
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You can try that yourself. Hold a small object like a coin at arm’s length and cover the Moon when it’s near the horizon. Try again when it’s higher in the sky. You’ll find that the object covers the same amount of the Moon both times. The difference lies not in the Moon’s position but in how your brain interprets the visual context.
The supermoon illusion, in itself, is a reminder that perception molds reality. It is that combination of natural brightness and mental trickery that makes these breathtaking views for fascinated skywatchers worldwide.
So the next time the Moon seems impossibly close, remember it hasn't changed its orbit. It's your mind painting a grander picture of the night sky.
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Disclaimer: This article explains the science behind the supermoon and Moon illusion. It is based on verified astronomical concepts and visual perception studies.
