When is the next moon illusion

Carefully analyzing photos of the moon as it rises also shows that it doesn't change. In fact, if anything, measurements show the moon actually takes up slightly less of the sky when it's on the horizon about 2 percent less, to be precise. That's because it really is slightly farther away from us. When the moon is straight above us, we're seeing it from the distance between it and the Earth, but when it's on the horizon, we're looking across an additional radius of the Earth:.

Not to scale. Bob King. So Aristotle was wrong. The Earth doesn't look bigger because of the sky. Instead, it's all in our minds. Recent MRI research has confirmed this. A study replicated a very similar illusion in a lab, and found that an object perceived to be larger and farther away shown at left produced a greater area of activation in the brain's visual map than the same object perceived to be closer and smaller shown at right — even though they're the exact same size:.

Murray et al. The object at left like the moon at the horizon isn't actually bigger — but our brains perceive it as bigger anyway. In the years since Aristotle, people have put forth dozens of competing hypotheses.

The most prominent one involves the way our brains figure out the size of objects at varying distances. The idea is that our brains are somehow compensating for perceived distance. For instance, when a car drives away from you, the amount of your visual field it takes up gets smaller and smaller, but you know the car isn't actually shrinking.

Your brain reconciles its distance with its apparent size so that the car appears the same size as it drives away. This gets trickier when we're looking at objects really far away, because we can't accurately perceive depth at such great distances.

So if we perceive the moon at the horizon as farther away than at the top of the sky, this same mechanism might trick us into thinking it looks bigger than it actually is. Damian Adrian. There have been a few hypotheses for why the moon might seem farther away at the horizon than elsewhere. Some suggest it's because we perceive the sky as a flattened dome , rather than a perfect hemisphere perhaps because we're used to seeing it filled by flat, relatively low cloud cover.

University of Manchester. Others propose it's because much of the time when we see the horizon, there are large objects say, fields or mountains in the foreground. We know mountains are huge, so the horizon must be distant. I believe the moon illusion results from what happens when the mechanism operates in an unusual situation. In normal perception, when rigid objects move in depth distance , the angular size of the light image stimulating our eyes grows or shrinks.

The brain automatically translates this changing stimulation back into the perception of rigid objects whose position in depth is changing. Because the moon is changing its apparent position in depth while the light stimulus remains constant, the brain's size-distance mechanism changes its perceived size and makes the moon appear very large. Sign up for our email newsletter. Already a subscriber? Sign in. Thus it's an illusion rooted in the way our brains process visual information.

Even though we've been observing it for thousands of years, there's still not a satisfying scientific explanation for exactly why we see it. Go out on the night of the full moon and find a good spot to watch it rise. It can be breathtaking, eliciting an awestruck "Wow! When we observe the Moon near the horizon, it often looks HUGE — whether it's peeking over the shoulder of a distant mountain, rising out of the sea, hovering behind a cityscape, or looming over a thicket of trees.

But here's the thing: it's all in your head. The Moon's seeming bigness is an actual illusion, rather than an effect of our atmosphere or some other physics.

You can prove it for yourself in a variety of ways. Hold up your outstretched index finger next to the Moon. You'll find that your fingernail and the Moon are about the same size. Or try looking at the Moon through a paper tube, or bend over and look backward between your legs. When you view it like this, the Moon will be nowhere near as big as it had seemed. Known as the apparent distance theory or the sky illusion, the explanation was made popular by Arab scientist Ibn al-Haytham.

He suggested that man-made and natural objects between an observer and the horizon create an illusion, where the observer inflates the distance between him and the horizon as compared to the distance between him and those directly above him. This leads to the observer believing that the horizon Moon is further away and bigger than the Moon at or close to the zenith.

Another version of the sky illusion is the flat sky theory or the apparent sky dome theory. According to this theory, the human brain perceives the sky above us not as a dome, but as a flattened dome, much like an inverted bowl. When the Moon is projected on this mental model of the flat sky, the brain sees the Moon at the horizon as bigger than the Moon on the top of the dome.

This is perhaps why pilots see a larger than usual Moon despite not having any intervening objects between them and the Moon. Scientific experiments have however proven that in general, people tend to presume that the Moon is bigger and closer to the Earth when on the horizon.

Different types of atmospheric phenomena. Similar to the sky illusion, the Ponzo illusion , named after Italian psychologist Mario Ponzo, suggests that when two identically sized lines are drawn across a pair of converging horizontal lines, the line at the top is thought to be bigger than the line at the bottom.

This is because to the human eye the top line seems to span a greater distance between the two converging lines. Some experts suggest that objects between the observer and the horizon Moon act as the converging line, tricking the mind into thinking that the Moon is bigger than it is.