The structure of the sun. Spectrum of solar radiation: description, features and interesting facts

life rays.

The sun emits three types of ultraviolet rays. Each of these types affects the skin differently.

Most of us feel more healthy and full of life after relaxing on the beach. Thanks to life-giving rays, vitamin D is formed in the skin, which is necessary for the full absorption of calcium. But only small doses of solar radiation have a beneficial effect on the body.

But heavily tanned skin is still damaged skin and, as a result, premature aging and a high risk of skin cancer.

Sunlight is electromagnetic radiation. In addition to the visible spectrum of radiation, it contains ultraviolet, which is actually responsible for tanning. Ultraviolet stimulates the ability of melanocyte pigment cells to produce more melanin, which performs a protective function.

Types of UV rays.

There are three types of ultraviolet rays, which differ in wavelength. Ultraviolet radiation is able to penetrate the epidermis of the skin into deeper layers. This activates the production of new cells and keratin, resulting in the skin becoming tougher and rougher. The sun's rays, penetrating the dermis, destroy collagen and lead to changes in the thickness and texture of the skin.

Ultraviolet rays a.

These rays have the lowest level of radiation. It used to be believed that they were harmless, however, it has now been proven that this is not the case. The level of these rays remains almost constant throughout the day and year. They even penetrate glass.

Type A UV rays penetrate through the layers of the skin, reaching the dermis, damaging the base and structure of the skin, destroying collagen and elastin fibers.

A-rays contribute to the appearance of wrinkles, reduce skin elasticity, accelerate the appearance of signs of premature aging, weaken the skin's defense system, making it more susceptible to infections and possibly cancer.

UV rays B.

Rays of this type are emitted by the sun only at certain times of the year and hours of the day. Depending on air temperature and geographic latitude, they usually enter the atmosphere between 10:00 and 16:00.

Type B UV rays cause more serious damage to the skin, as they interact with DNA molecules that are contained in skin cells. B-rays damage the epidermis, leading to sunburn. B-rays damage the epidermis, leading to sunburn. This type of radiation enhances the activity of free radicals, which weaken the natural defense system of the skin.

Ultraviolet B rays cause tanning and sunburn, lead to premature aging and the appearance of dark pigment spots, make the skin rough and rough, accelerate the appearance of wrinkles, and can provoke the development of precancerous diseases and skin cancer.

Prominence on the surface

The radiation from the sun, which is known as sunlight, is a mixture of electromagnetic waves ranging from infrared (IR) to ultraviolet (UV) rays. It includes visible light, which lies between IR and UV in the electromagnetic spectrum.

Velocity of propagation of electromagnetic waves

All electromagnetic waves (EM) propagate at a speed of approximately 3.0x10*8 m/s in a vacuum. Space is not a perfect vacuum, it actually contains low concentrations of particles, electromagnetic waves, neutrinos and magnetic fields. Since the average distance between the Earth and the Sun is more than 149.6 million km, it takes about 8 minutes for the radiation to reach the Earth. The sun shines not only in the IR, visible and UV range. Basically, it emits high-energy gamma rays.

However, gamma-ray photons travel a long way to the surface, they are constantly absorbed by the solar plasma and re-emitted with a change in their frequency.

By the time they reach the surface, gamma ray photons are in the IR, visible, and UV spectra. Infrared radiation is the heat that we feel. Without it and visible light, life on Earth would be impossible. During solar flares, it also emits X-rays. When the Sun's electromagnetic radiation reaches the Earth's atmosphere, some of it is absorbed while the rest reaches the Earth's surface.

In particular, UV radiation is absorbed by the ozone layer and re-emitted as heat, which leads to heating of the stratosphere.

The sun radiates its energy in all wavelengths, but in different ways. Approximately 44% of the radiation energy is in the visible part of the spectrum, and the maximum corresponds to the yellow-green color. About 48% of the energy lost by the Sun is carried away by infrared rays of the near and far range. Gamma rays, X-rays, ultraviolet and radio radiation account for only about 8%.

The visible part of solar radiation, when studied with the help of spectrum-analyzing instruments, turns out to be inhomogeneous - absorption lines are observed in the spectrum, first described by J. Fraunhofer in 1814. These lines arise when photons of certain wavelengths are absorbed by atoms of various chemical elements in the upper, relatively cold, layers of the Sun's atmosphere. Spectral analysis makes it possible to obtain information about the composition of the Sun, since a certain set of spectral lines characterizes a chemical element extremely accurately. So, for example, with the help of observations of the spectrum of the Sun, the discovery of helium was predicted, which was isolated on Earth later.

In the course of observations, scientists found that the Sun is a powerful source of radio emission. Radio waves penetrate into interplanetary space, which are emitted by the chromosphere (centimeter waves) and the corona (decimeter and meter waves). The radio emission of the Sun has two components - constant and variable (bursts, "noise storms"). During strong solar flares, the radio emission from the Sun increases thousands and even millions of times compared to the radio emission from the quiet Sun. This radio emission has a non-thermal nature.

X-rays come mainly from the upper layers of the chromosphere and the corona. The radiation is especially strong during the years of maximum solar activity.

The sun emits not only light, heat and all other types of electromagnetic radiation. It is also a source of a constant flow of particles - corpuscles. Neutrinos, electrons, protons, alpha particles, and heavier atomic nuclei all together make up the corpuscular radiation of the Sun. A significant part of this radiation is a more or less continuous outflow of plasma - the solar wind, which is a continuation of the outer layers of the solar atmosphere - the solar corona. Against the background of this constantly blowing plasma wind, individual regions on the Sun are sources of more directed, enhanced, so-called corpuscular flows. Most likely, they are associated with special regions of the solar corona - coronary holes, and also, possibly, with long-lived active regions on the Sun. Finally, the most powerful short-term particle fluxes, mainly electrons and protons, are associated with solar flares. As a result of the most powerful flashes, particles can acquire velocities that make up a significant fraction of the speed of light. Particles with such high energies are called solar cosmic rays.

Solar corpuscular radiation has a strong influence on the Earth, and above all on the upper layers of its atmosphere and magnetic field, causing many geophysical phenomena. The magnetosphere and the Earth's atmosphere protect us from the harmful effects of solar radiation.

Candidate of Physical and Mathematical Sciences E. LOZOVSKAYA.

With the onset of warm summer days, we are drawn to bask in the sun. Sunlight improves mood, stimulates the production of vital vitamin D in the skin, but at the same time, unfortunately, contributes to the appearance of wrinkles and increases the risk of skin cancer. A significant part of both beneficial and harmful effects is associated with that part of solar radiation that is invisible to the human eye - ultraviolet.

The spectrum of electromagnetic radiation and the spectrum of the sun. The boundary between ultraviolet B and C corresponds to the transmission of the earth's atmosphere.

Ultraviolet causes various damage to DNA molecules in living organisms.

The intensity of ultraviolet B depends on latitude and time of year.

Cotton clothing provides good UV protection.

The sun is the main source of energy for our planet, and this energy comes in the form of radiation - infrared, visible and ultraviolet. The ultraviolet region is located beyond the short-wavelength edge of the visible spectrum. When it comes to the effects on living organisms, there are usually three areas in the ultraviolet spectrum of the sun: ultraviolet A (UV-A; 320-400 nanometers), ultraviolet B (UV-B; 290-320 nm) and ultraviolet C (UV-C ; 200-290 nm). The division is quite arbitrary: the boundary between UV-B and UV-C is chosen on the basis that light with a wavelength of less than 290 nm does not reach the Earth's surface, since the earth's atmosphere, thanks to oxygen and ozone, acts as an effective natural light filter. The boundary between UV-B and UV-A is based on the fact that radiation shorter than 320 nm causes much more erythema (reddening of the skin) than light in the 320-400 nm range.

The spectral composition of sunlight largely depends on the time of year, weather, geographic latitude and height above sea level. For example, the farther from the equator, the stronger the short-wave boundary shifts towards long waves, since in this case the light falls on the surface at an oblique angle and travels a greater distance in the atmosphere, which means it is more absorbed. The thickness of the ozone layer also affects the position of the short-wave boundary, so more ultraviolet reaches the Earth's surface under the "ozone holes".

At noon, the intensity of radiation at a wavelength of 300 nm is 10 times higher than three hours before or three hours later. Clouds scatter ultraviolet, but only dark clouds can block it completely. Ultraviolet rays are well reflected from sand (up to 25%) and snow (up to 80%), worse from water (less than 7%). The ultraviolet flux increases with height, approximately 6% per kilometer. Accordingly, in places located below sea level (for example, off the coast of the Dead Sea), the radiation intensity is less.

LIFE UNDER THE SUN

Without light, life on Earth could not exist. Plants use solar energy, store it with the help of photosynthesis and provide energy through food to all other living beings. For humans and other animals, light provides the ability to see the world around them, regulates the biological rhythms of the body.

This cheerful picture is slightly complicated by ultraviolet, since its energy is enough to cause serious damage to DNA. Scientists have counted more than two dozen different diseases that occur or are aggravated by the action of sunlight, among them xeroderma pigmentosum, squamous cell skin cancer, basalioma, melanoma, cataracts.

Of course, in the process of evolution, our body has developed mechanisms to protect against ultraviolet radiation. The first barrier that blocks potentially dangerous radiation from entering the body is the skin. Almost all ultraviolet is absorbed in the epidermis, the outer layer of the skin with a thickness of 0.07-0.12 mm. Light sensitivity is largely determined by the body's inherited ability to produce melanin, a dark pigment that absorbs light in the epidermis and thereby protects the deeper layers of the skin from photodamage. Melanin is produced by specialized skin cells called melanocytes. UV radiation stimulates the production of melanin. This biological pigment is formed most intensively when irradiated with UV-B light. True, the effect does not appear immediately, but after 2-3 days after exposure to the sun, but it persists for 2-3 weeks. At the same time, the division of melanocytes is accelerated, the number of melanosomes (granules containing melanin) increases, and their size increases. Light in the UV-A range is also capable of causing a tan, but weaker and less persistent, since the number of melanosomes does not increase, but only photochemical oxidation of the melanin precursor to melanin occurs.

According to the susceptibility to sunlight, six types of skin are distinguished. Type I skin is very light, burns easily, and does not tan at all. Type II skin burns easily and becomes slightly tanned. Type III skin tans quickly and burns less. Type IV skin is even more resistant to sunlight. The skin of types V and VI is naturally dark (for example, in the natives of Australia and Africa) and is almost unaffected by the damaging effects of the sun. Blacks have a 100 times lower risk of developing non-melanoma skin cancer, and 10 times less melanoma than Europeans.

People with very fair skin are most vulnerable to UV exposure. In them, even a short stay in the bright sun causes erythema - redness of the skin. Erythema is caused mainly by UV-B radiation. As a measure of the effect of ultraviolet radiation on the body, such a concept as the minimum erythemal dose (MED) is often used, that is, one at which a slight redness is noticeable to the eye. In fact, the MED value is different not only in different people, but also in one person in different parts of the body. For example, for the skin of the abdomen of a white non-tanned person, the MED value is about 200 J/m 2 , and on the legs it is more than three times higher. Erythema usually occurs several hours after exposure. In severe cases, a real sunburn with blisters develops.

What substances in the epidermis, besides melanin, absorb ultraviolet radiation? Nucleic acids, amino acids tryptophan and tyrosine, urocanic acid. Nucleic acid damage is the most dangerous for the body. Under the action of light in the UV-B range, dimers are formed due to covalent bonds between adjacent pyrimidine (cytosine or thymine) bases. Since pyrimidine dimers do not fit into the double helix, this part of the DNA loses its ability to perform its functions. If the damage is small, special enzymes cut out the defective area (and this is another fairly effective defense mechanism). However, if the damage is greater than the cell's ability to repair, the cell dies. Outwardly, this is manifested in the fact that the burned skin "peels off". DNA damage can lead to mutations and, as a result, to cancer. Other molecular damage also occurs, for example, DNA cross-links with proteins. By the way, visible light contributes to the healing of damaged nucleic acids (this phenomenon is called photoreactivation). Antioxidants contained in the body help prevent the dangerous consequences of photochemical reactions.

Another consequence of ultraviolet radiation is immune suppression. Perhaps this reaction of the body is designed to reduce the inflammation caused by sunburn, but it also reduces resistance to infections. The photochemical reactions of urocanic acid and DNA serve as a signal for immune suppression.

FASHION FOR TANNING - A SYMBOL OF INDUSTRIAL SOCIETY

For a long time, white skin was considered a hallmark of the noble and rich: it was immediately clear that its owners did not have to work in the field from morning to night. But in the twentieth century, everything changed, the poor now spent whole days in factories and factories, and the rich could afford to relax in the fresh air, by the sea, showing a beautiful golden tan. After the Second World War, the fashion for tanning became massive; tanned skin began to be considered a sign of not only wealth, but also excellent health. The tourism industry has grown, offering holidays by the sea at any time of the year. But some time passed, and the doctors sounded the alarm: it turned out that the frequency of skin cancer among tan lovers increased several times. And as a lifesaver, it was suggested that everyone, without exception, use sunscreens and lotions, which include substances that reflect or absorb ultraviolet radiation.

It is known that even in the time of Columbus, the Indians used to paint themselves with red paint to protect themselves from the sun. Perhaps the ancient Greeks and Romans used a mixture of sand and vegetable oil for this purpose, since the sand reflected the sun's rays. The use of chemical sunscreens began in the 1920s when para-aminobenzoic acid (PABA) was patented as a sunscreen. However, it was soluble in water, so that the protective effect disappeared after bathing, and besides, it irritated the skin. In the 1970s, PABA was replaced by its esters, which are almost insoluble in water and do not cause severe irritation. The real boom in the field of sunscreen cosmetics began in the 1980s. Substances absorbing ultraviolet (in cosmetology, they were called "UV filters") began to be added not only to special "beach" creams, but also to almost all cosmetic products intended for use in the daytime: cream, liquid powder, lipstick.

According to the principle of operation, UV filters can be divided into two groups: reflecting light ("physical") and absorbing ("chemical"). Reflective agents include various kinds of mineral pigments, primarily titanium dioxide, zinc oxide, magnesium silicate. The principle of their action is simple: they scatter ultraviolet, preventing it from penetrating into the skin. Zinc oxide captures the wavelength range from 290 to 380 nm, the rest are somewhat smaller. The main disadvantage of reflective agents is that they are powder, opaque and give the skin a white color.

Naturally, cosmetics manufacturers were more attracted to transparent and highly soluble "chemical" UV filters (known in photochemistry as UV absorbers). These include the already mentioned PABA and its esters (now they are almost never used, since there is evidence that they decompose to form mutagens), salicylates, cinnamic acid derivatives (cinnamates), anthranilic esters, oxybenzophenones. The principle of operation of a UV absorber is that, having absorbed a quantum of ultraviolet radiation, its molecule changes its internal structure and converts light energy into heat. The most efficient and light-resistant UV absorbers operate on an intramolecular proton transfer cycle.

Most UV absorbers only absorb light in the UV-B region. Usually sunscreens contain not one UV filter, but several, both physical and chemical. The total content of UV filters can exceed 15 percent.

To characterize the protective effectiveness of creams, lotions and other cosmetic products, the so-called sun protection factor (in English "sun protection factor", or SPF) began to be used. The idea of ​​a sun protection factor was first proposed in 1962 by the Austrian scientist Franz Greiter and adopted by the cosmetics and pharmaceutical industries. The sun protection factor is defined as the ratio of the minimum dose of ultraviolet radiation required to cause erythema when exposed to protected skin to the dose that causes the same effect on unprotected skin. A popular interpretation has become widespread: if without protection you burn in 20 minutes, then by smearing your skin with a cream with a protective factor of, say, 15, you will get a sunburn only after being in the sun 15 times longer, that is, after 5 hours.

A FALSE SENSE OF PROTECTION

It would seem that a solution to the problem of ultraviolet radiation has been found. But in reality, everything is not so simple. In the scientific literature, reports began to appear that in people who constantly use sunscreens, the incidence of skin cancers such as melanoma and basalioma, not only did not decrease, but increased. Several explanations for this discouraging fact have been proposed.

First of all, scientists suggested that consumers use sunscreens incorrectly. When testing creams, it is customary to apply 2 mg of cream per 1 cm 2 to the skin. But, as studies have shown, people often apply a thinner layer, 2-4 times less, and the protection factor decreases accordingly. In addition, creams and lotions are partially washed off with water, for example during bathing.

There was also another explanation. As already noted, most chemical UV absorbers (namely, they are most widely used in cosmetics) absorb light only in the UV-B region, preventing the development of sunburn. But, according to some reports, melanoma occurs under the influence of UV-A radiation. By blocking UV-B radiation, sunscreens block the natural warning signal of skin redness, slow down the formation of a protective tan, and as a result, a person receives an excessive dose in the UV-A area, which can provoke cancer.

Survey results show that those who use sunscreens with a higher SPF spend more time in the sun and therefore unknowingly put themselves at greater risk.

We must not forget that a mixture of chemicals that are part of protective creams, with prolonged exposure to ultraviolet radiation, can become a source of free radicals - initiators of the oxidation of biomolecules. Some of the UV filters are potentially toxic or allergenic.

"SUNNY" VITAMIN

It is time to remember that in addition to the numerous negative effects of ultraviolet radiation, there are also positive ones. And the most striking example is the photosynthesis of vitamin D 3 .

The epidermis contains quite a lot of 7-dihydrocholesterol, a precursor of vitamin D 3 . Irradiation with UV-B light starts a chain of reactions, as a result of which cholecalciferol (vitamin D 3) is obtained, which is not yet active. This substance binds to one of the blood proteins and is transferred to the kidneys. There it is converted into the active form of vitamin D 3 - 1, 25-dihydroxycholecalciferol. Vitamin D 3 is necessary for calcium absorption in the small intestine, normal phosphorus-calcium metabolism and bone formation, with its deficiency, children develop a serious disease - rickets.

After irradiation of the whole body at a dose of 1 MED, the concentration of vitamin D 3 in the blood increases 10 times and returns to the previous level in a week. The use of sunscreens inhibits the synthesis of vitamin D 3 in the skin. The doses required for its synthesis are small. It is considered sufficient to spend about 15 minutes in the sun every day, exposing the face and hands to the sun's rays. The total annual dose required to maintain the level of vitamin D 3 is 55 MED.

Chronic deficiency of vitamin D 3 leads to weakening of bone tissue. The risk group includes dark-skinned children living in northern countries, and older people who are not much in the fresh air. Some researchers believe that the increase in the incidence of cancer with the use of sunscreens is associated precisely with blocking the synthesis of vitamin D 3 . It is possible that its deficiency leads to an increased risk of colon and breast cancer.

Other beneficial effects of ultraviolet radiation are mainly related to medicine. Diseases such as psoriasis, eczema, pink lichen are treated with ultraviolet light. The Danish physician Niels Finsen received the Nobel Prize in 1903 for the use of ultraviolet light in the treatment of lupus tuberculosis of the skin. The method of blood irradiation with ultraviolet is now successfully used to treat inflammatory and other diseases.

STRAW SUN HATS

The question of whether ultraviolet is useful or harmful does not have a clear answer: yes and no. Much depends on the dose, spectral composition and characteristics of the organism. Too much ultraviolet light is definitely dangerous, but you can't rely on protective creams. More research is needed to determine the extent to which sunscreen use may contribute to the development of cancer.

The best way to protect the skin from sunburn, premature aging, and at the same time reduce the risk of cancer is clothing. For ordinary summer clothes, protective factors above 10 are characteristic. Cotton has good protective properties, though in a dry form (when wet, it transmits more ultraviolet radiation). Don't forget a wide-brimmed hat and sunglasses.

The recommendations are quite simple. Avoid sun exposure during the hottest hours. Be especially careful with the sun if you are taking medications that have photosensitizer properties: sulfonamides, tetracyclines, phenothiazines, fluoroquinolones, non-steroidal anti-inflammatory drugs, and some others. Photosensitizers are also included in some plants, such as St. John's wort (see "Science and Life" No. 3, 2002). The effect of light can be enhanced by aromatic substances that are part of cosmetics and perfumes.

Given that scientists have doubts about the effectiveness and safety of sunscreens and lotions, do not use them (and daytime cosmetics with a high content of UV filters) unless absolutely necessary. If such a need arose, give preference to those means that provide protection in a wide range - from 280 to 400 nm. As a rule, such creams and lotions contain zinc oxide or other mineral pigments, so it makes sense to carefully read the composition on the label.

Sun protection should be individual, depending on the place of residence, season and skin type.