The physical phenomenon of a rainbow. What is a rainbow? How does she appear

The rainbow is usually explained by the simple refraction and reflection of the sun's rays in raindrops. Light emerges from the drop over a wide range of angles, but greatest intensity observed at an angle corresponding to the rainbow. visible light different wavelengths is refracted in a drop in different ways, that is, it depends on the wavelength of light (that is, color). A side rainbow is formed as a result of a double reflection of light inside each drop. In this case, the rays of light exit the drop at different angles than those that produce the main rainbow, and the colors in the secondary rainbow are in reverse order. The distance between the drops, which caused the rainbow, and the observer does not play a role

Typically, a rainbow is a colored arc with an angular radius of 42°, visible against the background of a curtain of heavy rain or rainfall streaks, often not reaching the Earth's surface. The rainbow is visible in the side of the sky opposite the Sun, and always with the Sun not covered by clouds.

The center of the rainbow is a point diametrically opposite to the Sun - the antisolar point. The outer arc of the rainbow is red, followed by orange, yellow, green arcs, etc., ending with the inner purple.

All rainbows are sunlight, decomposed into components and moved around the firmament in such a way that it seems to come from the part of the firmament opposite to that where the Sun is located.

The scientific explanation of the rainbow was first given by Rene Descartes in 1637. Descartes explained the rainbow on the basis of the laws of refraction and reflection of sunlight in drops of falling rain.

30 years later, Isaac Newton, who discovered the dispersion of white light upon refraction, supplemented Descartes' theory by explaining how colored rays are refracted in raindrops.

Despite the fact that Descartes - Newton's theory of the rainbow was created more than 300 years ago, it correctly explains the main features of the rainbow: the position of the main arcs, their angular dimensions, arrangement of colors in rainbows of various orders.

So, let a parallel beam of sunlight fall on a drop. Due to the fact that the surface of the drop is curved, different rays will have different angles of incidence. They vary from 0 to 90°. Let us trace the path of the beam passing through the drop. Having refracted at the air-water boundary, the beam enters the drop and reaches the opposite boundary. Part of the energy of the beam, refracted, leaves the drop, part, having experienced internal reflection, again goes inside the drop to the next place of reflection. Here again, part of the beam energy, having been refracted, leaves the drop, and some part, having experienced a second internal reflection, goes through the drop, etc. In principle, the beam can experience any number of internal reflections, and each beam has two refractions - at the entrance and at exit from the drop. A parallel beam of rays incident on a drop turns out to be strongly divergent upon exiting the drop (Fig. 2). The concentration of rays, and hence their intensity, is the greater, the closer they lie to the beam that has experienced the minimum deviation. Only the minimally deflected beam and the beams closest to it have sufficient intensity to form a rainbow. Therefore, this ray is called the ray of the rainbow.

Each white ray, refracted in a drop, decomposes into a spectrum, and a beam of divergent colored rays emerges from the drop. Since red rays have a lower refractive index than other colored rays, they will experience minimal deviation compared to the rest. The minimum deviations of the extreme color rays of the visible spectrum of red and violet are as follows: D1k \u003d 137 ° 30 "and D1ph \u003d 139 ° 20 \". The remaining colored rays will occupy intermediate positions between them.

The sun's rays that have passed through a drop with one internal reflection turn out to be emanating from points in the sky located closer to the antisolar point than to the Sun. Therefore, to see these rays, you must stand with your back to the Sun. Their distances from the antisolar point will be equal respectively: 180° - 137°30" = 42°30" for red and 180° - 139°20" = 40°40" for violet.

Why is the rainbow round? The fact is that a more or less spherical drop, illuminated by a parallel beam of rays of sunlight, can form a rainbow only in the form of a circle. Let's explain this.

The described path in the drop with a minimum deviation on leaving it makes not only the ray that we followed, but also many other rays that fell on the drop at the same angle. All these rays form a rainbow, which is why they are called rainbow rays.

How many rays of a rainbow are there in a beam of light falling on a drop? There are many of them, in fact, they form a whole cylinder. The locus of the points of their fall on the drop is a whole circle.

As a result of passing through the drop and refraction in it, the cylinder of white rays is transformed into a series of colored funnels inserted one into the other, centered at the antisolar point, with open bells facing the observer. The outer funnel is red, orange is inserted into it, yellow, then comes green, etc., ending with the inner violet.

Thus, each individual drop forms a whole rainbow!

Of course, the rainbow from one drop is weak, and in nature it is impossible to see it separately, since there are many drops in the curtain of rain. In the laboratory, it was possible to observe not one, but several rainbows formed by the refraction of light in one suspended drop of water or oil when illuminated by a laser beam.

The rainbow that we see in the sky is mosaic - it is formed by myriads of drops. Each drop creates a series of colored funnels (or cones) nested one on top of the other. But from a single drop, only one colored ray enters the rainbow. The observer's eye is a common point at which colored rays from many drops intersect. For example, all red rays that come out of different drops, but at the same angle and hit the observer's eye, form a red arc of the rainbow, and so do all orange and other colored rays. Therefore, the rainbow is round.

Two people standing side by side see each their own rainbow. If you walk along the road and look at the rainbow, it moves with you, being formed at every moment by the refraction of the sun's rays in more and more drops. Next, raindrops fall. The place of the fallen drop is occupied by another and manages to send its colored rays into the rainbow, followed by the next one, and so on. it's raining we see a rainbow.

This article will consider a wonderful phenomenon inherent in the Earth's atmosphere - a rainbow. About others atmospheric phenomena, such as the color of the sky, sunrise (sunset), northern (polar) lights, clouds can be read in separate articles in the Atmosphere section.

Description of the rainbow.

Rainbow represents a part of the circle line with the center (antisolar point) lying on the continuation of the straight line connecting the light source and the observer's eyes. Moreover, the sun is always behind the observer. Unlike a halo, it is impossible to see the sun and a rainbow at the same time.

If a rainbow is formed by raindrops, then it is usually observed at a distance of 1-2 kilometers from the observer. In the spray of a fountain or waterfall, this optical phenomenon can also be seen at closer distances.

During sunset or sunrise, the center of the rainbow circle is on the horizon line on the opposite side from the Sun, so the rainbow is a semicircle. As the sun's height above the horizon increases, so does the size of the rainbow. To an observer from the ground, the rainbow becomes invisible when the sun rises above the horizon above 42 degrees.

Actually, a rainbow is a full circle, but when viewed from earth's surface only part of its arc is visible. The higher a person rises, the most he observes circles. FROM high mountain or from an airplane you can see and full circle rainbows.

Colors of rainbow.

Colors of rainbow represent the colors of the spectrum, located from the outer edge to the inner: red, orange, yellow, green, cyan, indigo and violet. Stripes of different colors gradually pass into each other, i.e. In addition to the main listed colors, there are also many intermediate shades in the rainbow. It was the seven colors in the rainbow that he singled out for the first time Isaac Newton. Since then, we have traditionally adhered to this opinion. By the way, the Bulgarians do not agree with us - they distinguish only six colors in the rainbow, and the Chinese - five.

The appearance of the rainbow, its brightness and the width of the stripes depend on the size and number of water droplets. In large drops, an intense, pronounced, narrow rainbow is formed. With a decrease in the size of the droplets, the brightness of the rainbow also decreases, its bands expand and turn pale.

For the first time, he gave an explanation of the nature of the rainbow in 1637. He associated the formation of a rainbow with the reflection and refraction of light rays in drops of water.

The colors of the rainbow and the sequence of their arrangement were explained Isaac Newton in 1704. He discovered that light is refracted when passing into a medium with a different optical density, and decomposed white light into the colors of the spectrum using a glass prism.

The rainbow is formed in drops, the diameter of which is not more than 1 mm. A ray of the sun, falling on a drop, experiences one reflection and two refractions. As a result, it returns to the observer, already decomposed into the colors of the spectrum and from a different angle.

The figure shows a diagram of refraction and reflection in a drop of ten parallel rays of the same color, say, red. As can be seen from the figure, the beam marked with a dotted line emerges from the drop at an angle of 42 degrees to the sunlight. This beam, together with the rays adjacent to it, will form the red band of the rainbow. The rest of the rays are scattered by a wide fan under smaller angles, illuminating the area under the rainbow. That is why the sky under the rainbow always looks lighter than above it.

The beam of rays that forms a rainbow is called beam of Descartes named after the discoverer. We examined the scheme of refraction of ten rays, but Descartes at one time investigated, no less, no less than 10 thousand rays!

rainbow features.

An interesting feature of the rainbow is that every person sees your own rainbow . This is because we only see the reflected light that forms an angle of 42° with the Sun-Eye beam. It is clear that each person will have his own ray and, accordingly, his own rainbow-arc. When the position of the observer changes, the rainbow also moves.

Another interesting feature of the rainbow is that we see it all the time. in the same place . The drops that reflected the light for our rainbow fall to the ground, but others immediately come in their place, which, having reflected the sunlight for a moment, also disappear from our field of vision. That is why we see rainbows all the time when it is raining. But as soon as the rain weakens, the rainbow also turns pale, because the drops that send us their rainbow greetings become smaller.

Rainbow is one of the most amazing natural phenomena. What is a rainbow? How does she appear? These questions have interested people at all times. Even Aristotle tried to unravel its mystery. There are many beliefs and legends associated with it (the road to the next world, the connection between heaven and earth, a symbol of abundance, etc.). Some peoples believed that the one who passes under the rainbow will change their gender.

Her beauty amazes and delights. Looking at this colorful "magic bridge", I want to believe in miracles. The appearance of a rainbow in the sky notifies that the bad weather is over and a clear sunny time has come.

When does a rainbow happen? It can be observed during rain or after a downpour. But for its occurrence, lightning and thunder are not enough. It appears only if the sun breaks through the clouds. Certain conditions are needed in order for it to be noticed. It is necessary to be between the rain (it should be in front) and the sun (it should be behind). Your eyes, the center of the rainbow and the sun must be on the same line, otherwise you will not see this magical bridge!

Surely many have noticed what happens when a ray falls on a soap bubble or on the edge of a beveled mirror. It is divided into various colors (green, blue, red, yellow, purple, etc.). The object that breaks the beam into its component colors is called a prism. And the resulting multi-colored line is a spectrum.

So what is a curved spectrum, a colored band formed as a result of the separation of a beam of light when passing through raindrops (they are a prism in this case).

The colors of the solar spectrum are arranged in a certain order. On the one hand - red, then orange, next to it - yellow, green, blue, blue, purple. The rainbow is clearly visible as long as the raindrops fall evenly and frequently. The more often, the brighter it is. Thus, three processes occur simultaneously in a raindrop: refraction, reflection and decomposition of light.

Where to see a rainbow? At fountains, waterfalls, against the background of drops, splashes, etc. Its location in the sky depends on the position of the sun. You can admire the entire rainbow circle if you are high in the sky. The higher the sun rises above the horizon, the smaller the colored semicircle becomes.

The first attempt to explain what a rainbow is was made in 1611 by Antonio Dominis. His explanation was different from the biblical one, so he was sentenced to death. In 1637, Descartes gave a scientific phenomenon based on the refraction and reflection of sunlight. At that time, they did not yet know about the decomposition of the beam into a spectrum, that is, dispersion. Therefore, Descartes' rainbow turned out to be white. After 30 years, Newton "colored" it, supplementing his colleague's theory with explanations of the refraction of colored rays in raindrops. Despite the fact that the theory is more than 300 years old, it correctly formulates what a rainbow is, its main features (arrangement of colors, position of arcs, angular parameters).

It is amazing how light and water, which are familiar to us, create together a completely new, unimaginable beauty, a work of art given to us by nature. Rainbow always causes a surge of emotions and remains in memory for a long time.

In ancient times, due to lack of knowledge, people explained the wonders and beauties of nature with the help of myths and fairy tales. Then people did not have the opportunity to study the scientific justification for why it rained, hail or thunder. Similarly, people described everything unknown and distant, the appearance of a rainbow in the sky is no exception. IN ancient india the rainbow was the bow of the thunder god Indra, in Ancient Greece there was a virgin goddess Iris with a rainbow robe. In order to correctly answer the child how a rainbow appears, you first need to understand this issue yourself.

Scientific explanation of the rainbow

Most often, the phenomenon occurs during a small fine rain or immediately after it ends. After it, the smallest clots of fog remain in the sky. It is when the clouds disperse and the sun comes out that everyone can watch the rainbow with their own eyes. If it occurs during rain, then the colored arc consists of tiny drops of water. different size. Under the influence of light refraction, many small water particles form this phenomenon. If you watch a rainbow from a bird's eye view, then the color will not be an arc, but a whole circle.

In physics, there is such a thing as "dispersion of light", the name was given to it by Newton. Light dispersion is a phenomenon in which light is decomposed into a spectrum. Thanks to him, an ordinary white stream of light decomposes into several colors perceived by the human eye:

• Red;
• Orange;
• yellow;
• green;
• blue;
• blue;
• purple.

In the understanding of human vision, the colors of the rainbow are always seven and each of them is located in a certain sequence. However, the colors of the rainbow are continuous, they smoothly connect with each other, which means that it has many more shades than we can see.

Conditions for the appearance of a rainbow

To see a rainbow on the street, two main conditions must be met:

• a rainbow appears more often if the sun is low on the horizon (sunset or sunrise);
• you need to stand with your back to the sun and face the passing rain.

A multi-colored arc appears not only after or during rain, but also:

• watering the garden with a hose;
• while swimming in the water;
• in the mountains near the waterfall;
• in the city fountain in the park.

If the rays of light are reflected from the drop at the same time several times, a person manages to see a double rainbow. It is noticeable much less often than usual, the second rainbow is noticeable much worse than the first one and its color is in a mirror image, i.e. ends in purple.

How to make your own rainbow

To make a rainbow yourself, a person needs:

• a bowl of water;
• white sheet of cardboard;
• small mirror.

The experiment is carried out in sunny weather. To do this, a mirror is lowered into an ordinary bowl of water. The bowl is positioned so that the sunlight falling on the mirror is reflected on a sheet of cardboard. To do this, some time will have to change the angle of inclination of objects. Catching a tilt you can enjoy the rainbow.

Most fast way make a rainbow yourself - use an old CD. Change the angle of the disk in direct sunlight and get a clear bright rainbow.

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Rainbow types. What rainbow is?

A primary rainbow is a type of rainbow formed as a result of a single reflection of light.

As we already know, a rainbow occurs as a result of multiple internal reflections of light in water droplets. The more reflections experienced by a beam of light, the less energy it has.

Therefore, the brightest is a rainbow formed from rays that have experienced only one reflection. This so-called primary rainbow with a corner radius of 42°.

A polyrainbow is a type of rainbow formed as a result of multiple reflections of a ray of light in a drop of water.

Often over the first, or primary, rainbow, we observe the second, the so-called side or secondary rainbow , with an angular radius of 52°. Together these rainbows form polyrainbow or multiple rainbow .

When the Sun reaches an altitude of 42°, the primary rainbow is no longer visible. And when the Sun reaches a height of 52 °, the side one also disappears.

The primary rainbow is formed as a result of a single reflection of a beam of light in a drop of water. A secondary rainbow is a product of double reflection. Each reflection in the drop "flips" the beam, so the colors in the secondary rainbow are arranged in reverse order, i.e. the outer band is purple and the inner band is red.

Sometimes you can observe a third rainbow (angular radius of 60 °), and even a fourth and fifth. But this is already an extremely rare optical phenomenon in the atmosphere.

Alexander's stripe - is not a type of rainbow, but is studied during the passage of the topic "Types of the rainbow".

is the strip of sky between the primary and secondary rainbows. It got its name from the philosopher Alexander of Aphrodisias, who first described it in 200 AD.

The Alexander Strip appears darker than the surrounding sky. To explain this phenomenon, let us recall the drawing depicting Descartes' ray. As we remember, the rays that have experienced a single reflection illuminate the sky under the primary rainbow, leaving the drop at an angle of no more than 42.1 ° to the sun.

As a result of double reflection, the rays from the drop emerge at an angle greater than 50.9°, illuminating the sky above the secondary rainbow. That is, that region of the sky, which lies between 42.1 ° and 50.9 °, is not illuminated either during the primary or secondary rainbows. So it turns out that the strip of Alexander, about 9 ° wide, is darker than the rest of the sky.

A lunar rainbow is a type of rainbow formed by lunar rays.

You can watch a rainbow not only during the day, but also at night. In this case, the raindrops are no longer refracted Sun rays, but lunar.

It is no different from the sun, except for the brightness. To the human eye, due to the peculiarities of its structure, the lunar rainbow is most often seen as white. But in long exposure shots, you can also get colors.

Just like the solar rainbow, the lunar rainbow appears on the side opposite the moon, and the night luminary should be as low as possible above the horizon. The lunar rainbow appears only on nights when the moon is especially bright, namely on the full moon and nights close to it.

That is, for a lunar rainbow to appear, three conditions must be met:

Full moon;

Rising or setting of the moon;

Rain on the opposite side of the sky from the moon.

It is clear that all these conditions are rarely met simultaneously, and therefore the lunar rainbow is a very rare optical phenomenon in the atmosphere.

A red rainbow is a type of rainbow that forms at sunset.

If a rainbow appears at sunset, then there is such a phenomenon as red rainbow . It is sometimes unusually bright and visible even after sunset.

Why is the sunset rainbow red? The rays of the sun, passing through the thickness of the atmosphere, are scattered, and the intensity of the scattering of rays different color not the same. For example, shorter blue waves scatter 16 times more intensely than red ones, so the sky is blue during the day.

At sunset, the rays of the sun pass long haul in the atmosphere and shorter rays are scattered along the road. Only long waves of yellows, reds and oranges reach us. They form an optical phenomenon in the atmosphere - a red rainbow.

A dew rainbow is a type of rainbow that forms in drops of dew.

Sometimes in the early morning, just after sunrise, you can watch rainbow on dew .

Its formation mechanism is the same as that of an ordinary rainbow.

However, the shape of the rainbow on dew is not circular, but hyperbolic, which is characteristic feature this unusual look rainbows.

It is observed extremely rarely, but it is an unforgettable sight.

A double rainbow is a type of rainbow formed in raindrops of different sizes.

are two rainbow arcs starting at the same point.

She can come when it's raining mixed type- from large and small drops. Large drops flatten under their own weight, small ones remain the same shape.

These two types of droplets form two intersecting starting point arcs.

A rainbow wheel is a type of rainbow that forms when it rains heavily.

is a broken rainbow. Dark areas occur when going too heavy rain, preventing the light of the rainbow from reaching the observer's eyes. Also, dark clouds can participate in the formation of gaps.

The end result is a rainbow appearance like a cartwheel. And if the clouds are moving quickly at the same time, then the illusion of the “wheel” movement arises.

A foggy rainbow is a type of rainbow that forms in drops of fog.

misty rainbow also called white rainbow or foggy arc . It is a wide white arc, sometimes faintly colored along the edges. Outer side can be dyed in purple, and the inner one is orange. A white rainbow is formed in very small fog droplets with a radius of no more than 25 microns.

The nature of the white rainbow is different in that the drops that form this rainbow are much smaller than the drops that form an ordinary rainbow. The white color of the rainbow is associated with the phenomenon of light diffraction in water droplets. The smaller the droplet radius, the stronger influence diffraction. Diffraction, speaking in simple terms, this is a combination of light beams of different colors into one white. That is, if in large drops the light decomposes into components and forms an ordinary rainbow, then in small drops, on the contrary, it merges into one and forms a foggy rainbow.

In this article, we examined the Types of the rainbow and answered the question: What kind of rainbow happens? Read further: