The human eye perceives colors. Interesting facts about human eyes

are windows to the world and a mirror of our soul. But how well do we know our eyes?

Did you know how much our eyes weigh? Or how many shades of gray can we see?

Did you know that brown eyes are blue eyes with a brown layer on top?

Here are some interesting facts about eyes that will surprise you.

Human eye color

1. Brown eyes are actually blue under brown pigment. There is even a laser procedure that can turn brown eyes blue permanently.

2. The pupils of the eyes expand by 45 percent when we look at someone we love.

3. The cornea of ​​the human eye is so similar to the cornea of ​​a shark that the latter is used as a substitute for eye surgery.

4. You can't sneeze with your eyes open.

5. Our eyes can distinguish about 500 shades of gray.

6. Each eye contains 107 million cells, and they are all sensitive to light.

7. Every 12th male is colorblind.

8. Human eye sees only three colors: red, blue and green. The rest of the colors are combinations of these colors.

9. Our eyes are about 2.5 cm in diameter, and they weigh about 8 grams.

The structure of the human eye

10. Of all the muscles in our body, the muscles that control our eyes are the most active.

11. Your eyes will always stay the same size as at birth and the ears and nose never stop growing.

12. Only 1/6 of the eyeball is visible.

13. On average over a lifetime, we we see about 24 million different images.

14. Your fingerprints have 40 unique characteristics while your iris has 256. This is the reason why retinal scanning is used for security purposes.

15. People say "before the blink of an eye" because it's the fastest muscle in the body. Blinking lasts about 100 - 150 milliseconds, and you can blink 5 times per second.

16. Eyes process about 36,000 bits of information every hour.

17. Our eyes focus on about 50 things per second.

18. Our eyes blink an average of 17 times a minute, 14,280 times a day, and 5.2 million times a year.

19. The ideal duration of eye contact with the person you first met is 4 seconds. This is necessary to determine what color of eyes he has.

brain and eyes

20. We we see with the brain, not with the eyes. In many cases, blurry or poor vision is not caused by the eyes, but by problems with the visual cortex of the brain.

21. The images that are sent to our brain are actually upside down.

22. Eyes use about 65 percent of brain resources. This is more than any other part of the body.

23. Eyes began to develop about 550 million years ago. The simplest eye was particles of photoreceptor proteins in single-celled animals.

24. Each eyelash lives about 5 months.

26. The eyes of the octopus do not have a blind spot, they developed separately from other vertebrates.

27. Around 10,000 years ago everyone had brown eyes until a man living in the Black Sea region developed a genetic mutation that led to blue eyes.

28. The wriggling particles that appear in your eyes are called " floaters". These are shadows cast on the retina by tiny filaments of protein within the eye.

29. If you pour cold water into a person's ear, the eyes will move towards the opposite ear. If you pour warm water into an ear, the eyes will move to the same ear. This test, called the "caloric test", is used to determine brain damage.

Signs of eye disease

30. If in the flash photo you have only one eye red, there is a possibility that you have an eye tumor (if both eyes look in the same direction into the camera). Fortunately, the cure rate is 95 percent.

31. Schizophrenia can be diagnosed with up to 98.3 percent accuracy using a conventional eye movement test.

32. Humans and dogs are the only ones who look for visual cues in the eyes of others, and dogs only do this when interacting with humans.

33. Approximately 2 percent of women have a rare genetic mutation due to which they have an additional retinal cone. This allows them to see 100 million colors.

34. Johnny Depp is blind in his left eye and nearsighted in his right.

35. A case of Siamese twins from Canada, who have a common thalamus, has been recorded. Because of this, they could hear each other's thoughts and see through each other's eyes.

Facts about eyes and vision

36. The human eye can make smooth (not intermittent) movements only if it follows a moving object.

37. History cyclops appeared thanks to the peoples of the Mediterranean islands, who discovered the remains of extinct pygmy elephants. The skulls of elephants were twice the size of those of humans, and the central nasal cavity was often mistaken for the eye socket.

38. Astronauts can't cry in space due to gravity. Tears collect in small balls and begin to sting in the eyes.

39. Pirates used blindfold to quickly adapt vision to the environment above and below deck. Thus, one of their eyes got used to the bright light, and the other to the dim.

40. The flashes of light you see in your eyes when you rub them are called "phosphene".

41. There are colors that are too complex for the human eye, and they are called " impossible colors".

42. If you place two ping pong ball halves over your eyes and look at a red light while listening to a jamming radio, you will get bright and complex hallucinations. This method is called ganzfeld procedure.

43. We see certain colors, since this is the only spectrum of light that passes through the water - the area where our eyes appeared. There was no evolutionary reason on earth to see a wider spectrum.

44. Apollo astronauts have reported seeing flashes and streaks of light when they close their eyes. It was later revealed that this was caused by cosmic radiation bombarding their retinas outside of Earth's magnetosphere.

45. Sometimes people suffering from aphakia - the absence of the lens, report that see the ultraviolet spectrum of light.

46. ​​Bees have hairs in their eyes. They help determine wind direction and flight speed.

47. About 65-85 percent of white cats with blue eyes are deaf.

48. One of the firefighters of the Chernobyl disaster had brown eyes turned blue due to the strong radiation received. He died two weeks later from radiation poisoning.

49. To keep an eye on nocturnal predators, many animal species (ducks, dolphins, iguanas) sleep with one eye open. One half of their brain is asleep while the other is awake.

50. Almost 100 percent of people over 60 are diagnosed with herpes eye upon opening.

A person has the ability to see the world around him in all the variety of colors and shades. He can admire the sunset, emerald greenery, bottomless blue sky and other beauties of nature. The perception of color and its impact on the psyche and physical condition of a person will be discussed in this article.

What is color

Color is the subjective perception by the human brain of visible light, differences in its spectral structure, felt by the eye. In humans, the ability to distinguish colors is better developed than in other mammals.

Light affects the photosensitive receptors of the retina, and they then produce a signal transmitted to the brain. It turns out that the perception of color is formed in a complex way in the chain: the eye (neural networks of the retina and exteroreceptors) - the visual images of the brain.

Thus, color is an interpretation of the surrounding world in the human mind, resulting from the processing of signals from the light-sensitive cells of the eye - cones and rods. In this case, the former are responsible for the perception of color, and the latter for the sharpness of twilight vision.

"Color disorders"

The eye responds to three primary tones: blue, green, and red. And the brain perceives colors as a combination of these three primary colors. If the retina loses the ability to distinguish any color, then the person loses it. For example, there are people who are not able to distinguish from red. 7% of men and 0.5% of women have such features. It is extremely rare that people do not see the colors around at all, which means that the receptor cells in their retina do not function. Some suffer from weak twilight vision - this means that they have weakly sensitive rods. Such problems arise for various reasons: due to vitamin A deficiency or hereditary factors. However, a person can adapt to "color disorders", therefore, without a special examination, they are almost impossible to detect. People with normal vision are able to distinguish up to a thousand shades. The perception of color by a person varies depending on the conditions of the surrounding world. The same tone looks different in candlelight or sunlight. But human vision quickly adapts to these changes and identifies a familiar color.

Form perception

Cognizing nature, a person all the time discovered for himself new principles of the structure of the world - symmetry, rhythm, contrast, proportions. These impressions guided him, transforming the environment, creating his own unique world. In the future, the objects of reality gave rise to stable images in the human mind, accompanied by clear emotions. The perception of form, size, color is associated with the individual with the symbolic associative meanings of geometric shapes and lines. For example, in the absence of divisions, the vertical is perceived by a person as something infinite, incommensurable, directed upward, light. The thickening in the lower part or the horizontal base makes it more stable in the eyes of the individual. But the diagonal symbolizes movement and dynamics. It turns out that a composition based on clear verticals and horizontals tends to solemnity, static, stability, and an image based on diagonals tends to variability, instability and movement.

Double impact

It is generally recognized that the perception of color is accompanied by a strong emotional impact. This problem has been studied in detail by painters. V. V. Kandinsky noted that color affects a person in two ways. First, the individual is physically affected when the eye is either fascinated by a color or irritated by it. This impression is fleeting when it comes to familiar objects. However, in an unusual context (an artist's painting, for example), color can cause a strong emotional experience. In this case, we can talk about the second type of influence of color on the individual.

The physical effect of color

Numerous experiments by psychologists and physiologists confirm the ability of color to influence the physical state of a person. Dr. Podolsky described the visual perception of color by a person as follows.

• Blue color - has an antiseptic effect. It is useful to look at it with suppuration and inflammation. A sensitive individual helps better than green. But the "overdose" of this color causes some depression and fatigue.
• Green is hypnotic and pain-relieving. It has a positive effect on the nervous system, relieves irritability, fatigue and insomnia, and also raises the tone and blood.
• Yellow color - stimulates the brain, therefore it helps with mental deficiency.
• Orange color - has a stimulating effect and accelerates the pulse without raising blood pressure. It improves vitality, but over time can tire.
• Violet color - affects the lungs, heart and increases the endurance of body tissues.
• Red color - has a warming effect. It stimulates the activity of the brain, eliminates melancholy, but in large doses it irritates.

Kinds of color

The influence of color on perception can be classified in different ways. There is a theory according to which all tones can be divided into stimulating (warm), disintegrating (cold), pastel, static, deaf, warm dark and cold dark.

Stimulating (warm) colors promote arousal and act as irritants:

• red - life-affirming, strong-willed;
• orange - cozy, warm;
• yellow - radiant, contacting.

Disintegrating (cold) tones muffle excitement:

• purple - heavy, in-depth;
• blue - emphasizing the distance;
• light blue - guiding, leading into space;
• blue-green - changeable, emphasizing movement.

Reduce the impact of pure colors:

• pink - mysterious and gentle;
• lilac - isolated and closed;
• pastel green - soft, affectionate;
• gray-blue - restrained.

Static colors can balance and distract from exciting colors:

• pure green - refreshing, demanding;
• olive - softening, soothing;
• yellow-green - liberating, renewing;
• purple - pretentious, refined.

Silent tones promote concentration (black); do not cause excitation (gray); extinguish irritation (white).

Warm dark colors (brown) cause lethargy, inertia:

• ocher - softens the growth of arousal;
• earthy brown - stabilizes;
• dark brown - reduces excitability.

Dark cold tones suppress and isolate irritation.

Color and personality

The perception of color largely depends on the personal characteristics of a person. This fact was proved in his works on the individual perception of color compositions by the German psychologist M. Luscher. According to his theory, an individual who is in a different emotional and mental state can react differently to the same color. At the same time, the features of color perception depend on the degree of personality development. But even with a weak spiritual susceptibility, the colors of the surrounding reality are perceived ambiguously. Warm and light tones attract the eye more than dark ones. And at the same time, clear but poisonous colors cause anxiety, and a person’s vision involuntarily seeks a cold green or blue hue to rest.

Color in advertising

In an advertising appeal, the choice of color cannot depend only on the taste of the designer. After all, bright colors can both attract the attention of a potential client and make it difficult to obtain the necessary information. Therefore, the perception of the shape and color of the individual must necessarily be taken into account when creating advertising. Decisions can be the most unexpected: for example, against a colorful background of bright pictures, a person’s involuntary attention is more likely to be attracted by a strict black-and-white ad, rather than a colorful inscription.

Children and colors

Children's perception of color develops gradually. At first, they only distinguish warm tones: red, orange, and yellow. Then the development of mental reactions leads to the fact that the child begins to perceive blue, violet, blue and green colors. And only with age, the whole variety of color tones and shades becomes available to the baby. At three years old, children, as a rule, name two or three colors, and recognize about five. Moreover, some children have difficulty distinguishing the main tones even at the age of four. They poorly differentiate colors, hardly remember their names, replace the intermediate shades of the spectrum with the main ones, and so on. In order for a child to learn to adequately perceive the world around him, you need to teach him to correctly distinguish colors.

Development of color perception

Color perception should be taught from an early age. The baby is naturally very inquisitive and needs a variety of information, but it must be introduced gradually so as not to irritate the sensitive psyche of the child. At an early age, children usually associate color with the image of an object. For example, green is a Christmas tree, yellow is a chicken, blue is the sky, and so on. The teacher needs to take advantage of this moment and develop color perception using natural forms.

Color, as opposed to size and shape, can only be seen. Therefore, in determining the tone, a large role is given to comparison by superposition. If two colors are placed side by side, each child will understand if they are the same or different. At the same time, he still does not need to know the name of the color, it is enough to be able to complete tasks like "Plant each butterfly on a flower of the same color." After the child learns to visually distinguish and compare colors, it makes sense to start choosing according to the model, that is, to the actual development of color perception. To do this, you can use the book by G.S. Shvaiko called "Games and game exercises for the development of speech." Acquaintance with the colors of the surrounding world helps children feel reality more subtly and fully, develops thinking, observation, and enriches speech.

visual color

An interesting experiment on himself was set up by one resident of Britain - Neil Harbisson. Since childhood, he could not distinguish colors. Doctors found a rare visual defect in him - achromatopsia. The guy saw the surrounding reality as if in a black and white movie and considered himself a socially cut off person. One day, Neil agreed to an experiment and allowed himself to have a special cybernetic tool implanted in his head that allows him to see the world in all its colorful diversity. It turns out that the perception of color by the eye is not necessary at all. A chip and an antenna with a sensor were implanted in the back of Neal's head, which pick up vibration and convert it into sound. In addition, each note corresponds to a certain color: fa - red, la - green, do - blue and so on. Now, for Harbisson, a visit to a supermarket is akin to visiting a nightclub, and an art gallery reminds him of going to the Philharmonic. Technology gave Neil a sensation never seen before in nature: visual sound. A man makes interesting experiments with his new feeling, for example, he comes close to different people, studies their faces and composes music for portraits.

Conclusion

You can talk endlessly about the perception of color. An experiment with Neil Harbisson, for example, suggests that the human psyche is very plastic and can adapt to the most unusual conditions. In addition, it is obvious that people have a desire for beauty, which is expressed in an internal need to see the world in color, and not in monochrome. Vision is a unique and fragile tool that will take a long time to learn. It will be useful for everyone to learn about it as much as possible.

Therefore, perhaps it is time to take care of the health of the eyes. And since we are not able to reduce visual loads, it is worth at least more often unloading our eyes, giving them rest and performing simple visual tasks! For now, the facts.

1. Brown eyes have a blue base under a layer of dark pigment. There is even a kind of laser procedure that allows you to permanently turn any dark eyes into sky blue.

2. When looking at a loved one, our pupils dilate by 45%.

3. The cornea of ​​human eyes has many similarities with the cornea of ​​the eyes of a shark, so it is often used as a substitute for a human graft in transplant operations.

4. No one can sneeze with their eyes open.

5. A person can distinguish up to 500 shades of gray.

6. Our eye contains 107 million photosensitive cells.

7. Among men, one in 12 is color blind.

8. A person is able to perceive only three parts of the spectrum: blue, green, red. The variety of shades that we see is just derivatives of the named colors.

9. The diameter of the human eye is approximately 2.5 cm, and it weighs up to 8 grams.

10. The most active muscles in the human body are those that control the eyes.

11. The eyes forever remain the same size as at birth, and the ears and nose grow throughout life.

12. Like an iceberg, only 1/6 of it is visible to us.

13. In a lifetime, a person sees about 24 million different images.

The eye movement test can detect schizophrenia with an accuracy of up to 98.3%.

14. There are 40 unique characteristics found in human fingerprints and 256 in the iris. Therefore, in recent times, security scanning has become more and more common.

15. The catchphrase “you won’t have time to blink an eye” is very true, because the eye is the fastest muscle in our body. Blinking lasts from 100 to 150 milliseconds, which means that we can blink up to 5 times per second.

16. Every hour, the eyes transmit a huge amount of information to the brain. The bandwidth of this channel can be comparable to the channels of Internet providers in a large city.

17. Our eyes are capable of about 50 objects every second.

18. The images that our brain takes in come in upside down.

19. The eye-loaded brain works more than the rest of our body.

20. Human lives for about 5 months.

21. The Mayan tribes perceived it as something attractive, and tried to develop it in children.

22. About 10 thousand years ago, all people had brown eyes, until a person who lived near the Black Sea received a genetic mutation that led to the appearance of blue eyes.

23. When only one eye turns red in a flash photo, there is a chance that the remaining normal eye is affected by a tumor. Fortunately, the cure rate for eye tumors, if detected early, is about 95%.

24. The eye movement test can detect schizophrenia with an accuracy of up to 98.3%.

25. The only ones who are able to find clues in the eyes of others are dogs and people, however, dogs do this only when communicating with people.

26. 2% of women have a rare genetic mutation - additional, which allows you to see about 100 million colors.

27. The famous Johnny Depp is blind in his left eye, but short-sighted in his right.

28. A pair of Siamese twins from Canada had a common thalamus. This allowed them to listen to each other's thoughts, as well as see through the eyes of the other twin.

29. is able to draw a continuous line only when following an object in motion.

30. Stories about the Cyclopes appeared thanks to the peoples of the Mediterranean, who discovered the remains of long-extinct pygmy elephants. The skulls of elephants were twice as large as those of humans, and the central nasal cavity was often mistaken for it.

31. Astronauts don't cry in space just because of gravity. Tears, gathered in small balls, sting eyes.

32. Pirates, as a rule, were not one-eyed at all. An eye patch is nothing more than a way of adapting vision to the space above deck as well as below it. One eye got used to the bright light, the other to the semi-darkness.

33. The human eye is not able to distinguish the entire color spectrum, there are too “complex” colors for the human eye, they are called “impossible colors”.

34. We are able to see only certain colors, due to the fact that this is the only light spectrum that passes through the water, because that is where our ancestors appeared. There were no evolutionary reasons to recognize a wider spectrum on earth.

35. The development of the eyes began on earth about 550 million years ago. The most primitive eye was the protein particles of photoreceptors of unicellular animals.

36. People suffering

An ordinary person distinguishes about 150 primary colors, a professional - up to 10-15 thousand colors, under certain conditions, the human eye really distinguishes several million color valences, so they make tables for American astronauts. Figures may vary based on training, individual condition, lighting conditions, and other factors.
If you believe the source - "Biology in Questions and Answers" - The Color Space "of a normal person contains about 7 million different valences, including a small category of achromatic and a very extensive class of chromatic ones. The chromatic valencies of the surface color of an object are characterized by three phenomenological qualities: tone, saturation, and lightness. In the case of luminous color stimuli, "lightness" is replaced by "brightness". Ideally, color tones are "pure" colors. Hue can be mixed with an achromatic valence to give different shades of color. Hue saturation is a measure of the relative content of chromatic and achromatic components in it, and lightness is determined by the position of the achromatic component on the gray scale.

Studies have shown that in the visible region of the spectrum, the human eye is able to distinguish, under favorable conditions, about 100 shades of the color background. Over the entire spectrum, supplemented by pure purple colors, in conditions of sufficient brightness for color discrimination, the number of distinguishable shades in color tone reaches 150.

It has been empirically established that the eye perceives not only the seven primary colors, but also a huge variety of intermediate shades of color and colors obtained from mixing light of different wavelengths. In total, there are up to 15,000 color tones and shades.

An observer with normal color vision, when comparing differently colored objects or different light sources, can distinguish a large number of colors. A trained observer distinguishes about 150 colors by hue, about 25 by saturation, and by lightness from 64 in high light to 20 in low light.

Apparently, the inconsistency in the reference data is due to the fact that the perception of color can partially change depending on the psychophysiological state of the observer, the degree of his fitness, lighting conditions, etc.

Information

Visible radiation- electromagnetic waves perceived by the human eye, which occupy a portion of the spectrum with a wavelength of approximately 380 to 740 nm. Such waves occupy the frequency range from 400 to 790 terahertz. Electromagnetic radiation with these wavelengths is also called visible light, or simply light. The first explanations of the spectrum of visible radiation were given by Isaac Newton in the book "Optics" and Johann Goethe in the work "Theory of Colors", but even before them, Roger Bacon observed the optical spectrum in a glass of water.

Eye- a sensory organ of humans and animals, which has the ability to perceive electromagnetic radiation in the light wavelength range and provides the function of vision. About 90% of the information from the outside world comes through the human eye. Even the simplest invertebrates have the ability to phototropism due to their, albeit extremely imperfect, vision.

August 17th, 2015 09:25 am

We invite you to learn about the amazing properties of our vision - from the ability to see distant galaxies to the ability to capture seemingly invisible light waves.

Take a look around the room you are in - what do you see? Walls, windows, colorful objects - it all seems so familiar and self-evident. It is easy to forget that we see the world around us only thanks to photons - light particles reflected from objects and falling on the retina of the eye.

There are approximately 126 million light-sensitive cells in the retina of each of our eyes. The brain deciphers the information received from these cells about the direction and energy of photons falling on them and turns it into a variety of shapes, colors and intensity of illumination of surrounding objects.

Human vision has its limits. So, we are not able to see the radio waves emitted by electronic devices, nor to see the smallest bacteria with the naked eye.

Thanks to advances in physics and biology, it is possible to define the limits of natural vision. "Any object we see has a certain 'threshold' below which we stop distinguishing it," says Michael Landy, professor of psychology and neuroscience at New York University.

Let's first consider this threshold in terms of our ability to distinguish colors - perhaps the very first ability that comes to mind in relation to vision.

Our ability to distinguish, for example, violet from purple is related to the wavelength of photons that hit the retina of the eye. There are two types of light-sensitive cells in the retina - rods and cones. The cones are responsible for color perception (so-called day vision), while the rods allow us to see shades of gray in low light - for example, at night (night vision).

In the human eye, there are three types of cones and a corresponding number of types of opsins, each of which is particularly sensitive to photons with a certain range of light wavelengths.

S-type cones are sensitive to the violet-blue, short wavelength part of the visible spectrum; M-type cones are responsible for green-yellow (medium wavelength), and L-type cones are responsible for yellow-red (long wavelength).

All of these waves, as well as their combinations, allow us to see the full range of colors in the rainbow. "All sources of human-visible light, with the exception of a number of artificial ones (such as a refractive prism or a laser), emit a mixture of wavelengths," says Landy.

Of all the photons that exist in nature, our cones are able to capture only those that are characterized by a wavelength in a very narrow range (usually from 380 to 720 nanometers) - this is called the visible radiation spectrum. Below this range are infrared and radio spectra - the wavelength of low-energy photons of the latter varies from millimeters to several kilometers.

On the other side of the visible wavelength range is the ultraviolet spectrum, followed by the X-ray, and then the gamma-ray spectrum with photons whose wavelength does not exceed trillionths of a meter.

Although the vision of most of us is limited to the visible spectrum, people with aphakia - the absence of the lens in the eye (as a result of cataract surgery or, less commonly, a birth defect) - are able to see ultraviolet waves.

In a healthy eye, the lens blocks ultraviolet wavelengths, but in its absence, a person is able to perceive wavelengths up to about 300 nanometers as a blue-white color.

A 2014 study notes that, in a sense, we can all see infrared photons as well. If two of these photons hit the same retinal cell almost simultaneously, their energy can add up, turning invisible wavelengths of, say, 1000 nanometers into a visible wavelength of 500 nanometers (most of us perceive wavelengths of this wavelength as a cool green color) .

How many colors do we see?

In a healthy human eye, there are three types of cones, each of which is capable of distinguishing about 100 different color shades. For this reason, most researchers estimate the number of colors we can distinguish at about a million. However, the perception of color is very subjective and individual.

Jameson knows what he's talking about. She studies the vision of tetrachromats - people with truly superhuman abilities to distinguish colors. Tetrachromacy is rare, mostly in women. As a result of a genetic mutation, they have an additional, fourth type of cones, which allows them, according to rough estimates, to see up to 100 million colors. (Color blind people, or dichromats, have only two types of cones—they can see no more than 10,000 colors.)

How many photons do we need to see a light source?

In general, cones require much more light to function optimally than rods. For this reason, in low light, our ability to distinguish colors drops, and sticks are taken to work, providing black and white vision.

In ideal laboratory conditions, in areas of the retina where rods are largely absent, cones can fire when hit by just a few photons. However, sticks do an even better job of capturing even the dimmest light.

As experiments first carried out in the 1940s show, one quantum of light is enough for our eye to see it. "A person is only able to see a single photon," says Brian Wandell, professor of psychology and electrical engineering at Stanford University. "More retinal sensitivity just doesn't make sense."

In 1941, researchers from Columbia University conducted an experiment - the subjects were brought into a dark room and given their eyes a certain time to adapt. Sticks take several minutes to reach full sensitivity; that is why, when we turn off the light in the room, we lose the ability to see anything for a while.

Then, a flashing blue-green light was directed at the faces of the subjects. With a probability higher than normal chance, the participants in the experiment recorded a flash of light when only 54 photons hit the retina.

Not all photons reaching the retina are registered by photosensitive cells. Given this circumstance, the scientists came to the conclusion that just five photons activating five different rods in the retina are enough for a person to see a flash.

The smallest and most distant visible objects

The following fact may surprise you: our ability to see an object does not depend at all on its physical size or distance, but on whether at least a few photons emitted by it hit our retina.

“The only thing the eye needs to see anything is a certain amount of light emitted or reflected back to it by an object,” says Landy. “It all comes down to the number of photons reaching the retina. exists for a fraction of a second, we can still see it if it emits enough photons."

Psychology textbooks often state that on a cloudless dark night, the flame of a candle can be seen from a distance of up to 48 km. In reality, our retina is constantly bombarded with photons, so that a single quantum of light emitted from a great distance will simply be lost in their background.

To imagine how far we can see, let's take a look at the night sky, studded with stars. The sizes of the stars are enormous; many of those we see with the naked eye are millions of kilometers in diameter.

However, even the closest stars to us are located at a distance of more than 38 trillion kilometers from the Earth, so their apparent sizes are so small that our eye is not able to distinguish them.

On the other hand, we still observe stars as bright point sources of light, because the photons emitted by them overcome the gigantic distances separating us and hit our retinas.

All individual visible stars in the night sky are in our galaxy - the Milky Way. The farthest object from us that a person can see with the naked eye is located outside the Milky Way and is itself a star cluster - this is the Andromeda Nebula, located at a distance of 2.5 million light years, or 37 quintillion km, from the Sun. (Some people claim that on particularly dark nights, sharp vision allows them to see the Triangulum Galaxy, located at a distance of about 3 million light years, but let this statement remain on their conscience.)

The Andromeda Nebula contains one trillion stars. Due to the great distance, all these luminaries merge for us into a barely distinguishable speck of light. At the same time, the size of the Andromeda Nebula is colossal. Even at such a gigantic distance, its angular size is six times the diameter of the full moon. However, so few photons reach us from this galaxy that it is barely visible in the night sky.

Visual acuity limit

Why can't we see individual stars in the Andromeda Nebula? The fact is that the resolution, or acuity, of vision has its limitations. (Visual acuity refers to the ability to distinguish elements such as a point or a line as separate objects that do not merge with neighboring objects or with the background.)

In fact, visual acuity can be described in the same way as the resolution of a computer monitor - in terms of the minimum size of pixels that we can still distinguish as individual points.

Visual acuity limits depend on several factors - such as the distance between individual cones and rods in the retina. An equally important role is played by the optical characteristics of the eyeball itself, due to which not every photon hits a photosensitive cell.

In theory, studies show that our visual acuity is limited by our ability to see around 120 pixels per angular degree (a unit of angular measurement).

A practical illustration of the limits of human visual acuity can be an object the size of a fingernail located at arm's length, with 60 horizontal and 60 vertical lines of alternating white and black colors applied on it, forming a kind of chessboard. "It's probably the smallest drawing that the human eye can still make out," says Landy.

The tables used by ophthalmologists to check visual acuity are based on this principle. The most famous Sivtsev table in Russia consists of rows of black capital letters on a white background, the font size of which becomes smaller with each row.

The visual acuity of a person is determined by the size of the font at which he ceases to clearly see the contours of the letters and begins to confuse them.

It is the limit of visual acuity that explains the fact that we are not able to see with the naked eye a biological cell, the size of which is only a few micrometers.

But don't fret about it. The ability to distinguish a million colors, pick up single photons, and see galaxies a few quintillion kilometers away is a very good result, given that our vision is provided by a pair of jelly-like balls in the eye sockets, connected to a one and a half kilogram porous mass in the skull.