In the illusion, you have a scene where two lines are converging, like railroad tracks stretching away into the distance. Perhaps trees, mountains, and buildings help to trick your brain into thinking the Moon is both closer and bigger than it is? There's an effect discovered a century ago called the Ponzo illusion that describes how this works.
There's also some thinking that objects in the foreground of your lunar view play a role. It seems that our brains don't know that the Moon's distance doesn't change that much no matter where it is in the sky on a given night.
In general, the proposed explanations have to do with a couple of key elements of how we visually perceive the world: how our brains perceive the size of objects that are nearer or farther away, and how far away we expect objects to be when they're close to the horizon. But despite the fact that people have been observing this illusion for thousands of years, we still don't have a rock-solid scientific explanation for it. Depending on your mindset, this news might be unsatisfying, or it could be a reason to marvel at our mysterious brains. (Dust or pollution can also deepen the reddish color.) Why do we see the Moon illusion?īrace yourself: we don't really know. As it travels a longer path, more of the shorter, bluer wavelengths of light are scattered away, leaving more of the longer, redder wavelengths.
This happens because the Moon's light travels a longer distance through the atmosphere. It tends to have a more yellow or orange hue, compared to when it's high overhead. There's one notable way in which the Moon's appearance is actually different when it's low in the sky. The Moon DOES look more yellow near the horizon
Nasa picture of the day for tablets full#
This full Moon was the first of three consecutive supermoons. In other words, the Moon looks bigger in those photos because it's a zoomed-in view.Ī supermoon rises Dec. So, remember when you see dazzling photos that feature a giant Moon above the landscape: those images are created by zooming in on distant objects near the ground. Photographers can simulate the Moon illusion by taking pictures of the Moon low on the horizon using a long lens, with buildings, mountains, or trees in the frame. This is the result of the atmosphere acting like a weak lens.) (It may actually appear a little bit squashed in the vertical direction when it's near the horizon. If you keep your camera zoom settings the same, you'll find that the Moon is the same width, side to side, in both photos. When you view it like this, the Moon will be nowhere near as big as it had seemed.Īnother ironclad way to size-check the Moon is to take a photo when it's near the horizon, and another when it's high in the sky. Or try looking at the Moon through a paper tube, or bend over and look backward between your legs. You'll find that your fingernail and the Moon are about the same size. Hold up your outstretched index finger next to the Moon.
You can prove it for yourself in a variety of ways. The Moon's seeming bigness is an actual illusion, rather than an effect of our atmosphere or some other physics. 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.īut here's the thing: it's all in your head. It can be breathtaking, eliciting an awestruck "Wow!" from any skywatcher. Go out on the night of the full moon and find a good spot to watch it rise.
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