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200 votes
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Seeing something from only one angle means you have only seen (what?)% of its surface area at most?

There is no such upper bound. As a simple counter-example, consider a thin right-angled solid cone of base radius $r$ and height $h$, observed on-axis from some large(ish) distance $z$ away from the ...
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196 votes

Seeing something from only one angle means you have only seen (what?)% of its surface area at most?

As a completely tangential type of answer. Consider a neutron star; due to the General Relativistic bending of light in curved space we are not bounded by the dull constraints of Euclidean geometry! ...
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182 votes
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Why does a yellow object turn white under a yellow light? Shouldn't it turn yellow instead?

Your brain adjusts your perception of color to compensate for lighting that is strongly tinted. This was the reason for the violent conflict some time back about a certain dress. Depending on whether ...
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119 votes
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Could Legolas actually see that far?

Fun question! As you pointed out, $$\theta \approx 1.22\frac{\lambda}{D}$$ For a human-like eye, which has a maximum pupil diameter of about $9\ \mathrm{mm}$ and choosing the shortest wavelength in ...
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115 votes

Would visible light still be in a separate classification if we saw "colors" in a different wavelength?

Something special about the visible range is that water has low absorption in this range. It’s a rather sharp dip near the visible region. Since we know that life began in water, the beings that were ...
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90 votes
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How does light combine to make new colours?

Color perception is entirely a biological (and psychological) response. The combination of red and green light looks indistinguishable, to human eyes, from certain yellow wavelengths of light, but ...
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82 votes

If I can see someone's eyes, can they see mine?

Fermat's principle says that the direction of travel for any light ray can be reversed. Therefore there is always a line of sight between a pair of eyes in both ways. If one person is in the dark, ...
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68 votes

How many atoms does it take for us to perceive colour?

There are a couple of issues here. A pink (#FF00FF) object appears pink not because each atom is pink (there is no wavelength of light that is perceived to be the same pink by the ordinary human eye. ...
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65 votes
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How do photons get into the eyes?

Yes - we are surrounded by a "sea of photons". An individual object that reflects light (let's assume a Lambertian reflector - something that reflects incident photons in all directions) sends some ...
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62 votes
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Why do I see better under water using swimming goggles?

Is blurred effect due to turbulence? No, it is not. The turbulence has a little effect here. Even if there is no turbulence, one see everything blurred underwater. The reason is explained below. ...
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61 votes
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Why can we only "see" reflected light?

The key is that light must enter the eye for you to see something. You cannot see a beam of light from a low powered laser which is not directed into your eye if the air through which the light is ...
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56 votes
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How can we see a beam of light?

You're not seeing the photons in the beam that are traveling from A to B (beam starting point to beam destination), you are seeing photons that are scattering off of dust particles that are in the ...
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55 votes
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Musical notes and colors of a rainbow

On the most basic level, the answer is a flat no. The seven primary notes in an octave is specific to the western musical tradition. It's not entirely arbitrary as you say, but there are many other ...
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48 votes

Can you be blinded by a 'dim' light?

Yes indeed, infrared light (the wavelengths beyond those of red light) can be very harmful to your eyes even though you don't see them. The same applies for ultraviolet light (the wavelengths beyond ...
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45 votes
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Why are green screens green?

It's partly about how human colour vision works, partly about avoiding colours you want to keep, such as those of the actors. Colour cameras record concentrations of red, green and blue light to ...
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43 votes

If I can see someone's eyes, can they see mine?

The answer of Martin Ueding is correct if there is no intermediate image in the light path. For example, if you use a camera obscura, in general there will in be no way for the observed person to ...
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43 votes

Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

You are correct that almost always it is the UV content of sunlight and not its power that is the main hazard in staring at the Sun. The lighting during a total eclipse is one of those situations ...
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43 votes

Why am I able to see objects within 25 cm?

The least distance of distinct vision is the minimum distance your eye lens can focus on an object without any strain. This means the eye is in a relaxed state. But eye is a self adjusting lens. When ...
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43 votes

Why can't the human eye focus to make blurry photos/video clear?

The human eye focusing is resolving all the possible detail it can from a scene that is sharp and not distorted. The details of exactly how your brain forms an image from what your eye does is ...
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42 votes
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Why does a moving fan seem transparent?

The eyes are measuring the number of photons of each color that are hitting a given point of the retina – that are coming from some direction. This is a function of time, $f(t)$, for each point. ...
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42 votes
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How is it possible for other animals to have better night vision than humans, who can detect individual photons?

That research shows that humans can detect single photons, not that we're particularly good at it. Averaging across subjects’ responses and ratings from a total of 30,767 trials, 2,420 single-...
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42 votes

Why can we only "see" reflected light?

The reflected light is moving toward/into your eye, while the light just passing by you isn't. You can see light that's not "reflected", like the light emitted by a light bulb, there's nothing special ...
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  • 108k
41 votes

Why can't the human eye focus to make blurry photos/video clear?

Here's an explanation using geometric optics. I'll replace the human eye, which has a quasirandom scattering of light sensors on a curved surface, with a digital camera that has a regular grid of ...
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40 votes
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Does pure yellow exist in variations we can't discern?

Our ability to separate different colors from each others depends crucially on how many different receptors we have for colored light. Humans have three different receptors for light, which means ...
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38 votes
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Can a human size object move so fast that it ceases to be observable?

Let me start by clarifying that I assume the question is whether a superhuman or any object of human size can render itself invisible through speed alone. And that the speed of said object must be $v\...
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36 votes
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Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

The damage to your eyes comes from the total energy from the visible and near - infrared region even when you wear a 100% UV blocked sunglasses. When you look at the sun in normal days, the visible ...
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36 votes

Can you create white light by combining cyan wavelengths (490-520nm) with red wavelengths (630-700nm)?

Yes, but not with equal amounts of each. In order to answer this, we need to understand the CIE 1931 color space, and think about its algebraic properties. Essentially what the CIE specification says ...
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35 votes

Would visible light still be in a separate classification if we saw "colors" in a different wavelength?

The range of visible light wavelengths has a special property that makes it the commonly used range for all life forms on the Earth: It is the range of electromagnetic wavelengths that are short ...
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34 votes
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How do we see? Where do the photons disappear?

From the wiki article on color vision as an illustration of how photons are absorbed: Perception of color begins with specialized retinal cells containing pigments with different spectral ...
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