Photosphere and chromosphere of the Sun. Atmosphere of the Sun The temperature of the photosphere of the sun is approximately 6000 K

Photosphere is the main part of the solar atmosphere in which visible radiation is formed, which is continuous. Thus, it emits almost all of the solar energy that comes to us.

The photosphere is a thin layer of gas several hundred kilometers long, quite opaque.

The photosphere is visible when directly observing the Sun in white light in the form of its apparent “surface”.

The photosphere strongly emits, and therefore absorbs, radiation throughout the entire visible continuous spectrum.

For each layer of the photosphere located at a certain depth, its temperature can be found. The temperature in the photosphere increases with depth and is on average 6000 K.

The length of the photosphere is several hundred km.

The density of the photosphere substance is 10 -7 g/cm 3 .

1 cm 3 of the photosphere contains about 10 16 hydrogen atoms. This corresponds to a pressure of 0.1 atm.

Under these conditions, all chemical elements with low ionization potentials are ionized. Hydrogen remains in a neutral state.

The photosphere is the only region of neutral hydrogen on the Sun.

Visual and photographic observations of the photosphere reveal its fine structure, reminiscent of closely spaced cumulus clouds. Light round formations are called granules, and the entire structure is called granulation. The angular dimensions of the granules are no more than 1” arc, which corresponds to 700 km. Each individual granule exists for 5-10 minutes, after which it disintegrates and new granules form in its place. The granules are surrounded by dark spaces. The substance rises in the granules and falls around them. The speed of these movements is 1-2 km/s.

Granulation is a manifestation of the convective zone located under the photosphere. In the convective zone, mixing of matter occurs as a result of the rise and fall of individual masses of gas.

The reason for the occurrence of convection in the outer layers of the Sun is two important circumstances. On the one hand, the temperature directly below the photosphere increases very quickly in depth and radiation cannot ensure the release of radiation from deeper hot layers. Therefore, energy is transferred by the moving inhomogeneities themselves. On the other hand, these inhomogeneities turn out to be tenacious if the gas in them is not completely, but only partially ionized.

When passing into the lower layers of the photosphere, the gas is neutralized and is not able to form stable inhomogeneities. therefore, in the very upper parts of the convective zone, convective movements are slowed down and convection suddenly stops.

Oscillations and disturbances in the photosphere generate acoustic waves.

The outer layers of the convective zone represent a kind of resonator in which 5-minute oscillations are excited in the form of standing waves.

17.5 Outer layers of the solar atmosphere: chromosphere and corona. Causes and mechanism of heating of the chromosphere and corona.

The density of matter in the photosphere quickly decreases with height and the outer layers turn out to be very rarefied. In the outer layers of the photosphere, the temperature reaches 4500 K, and then begins to rise again.

There is a slow increase in temperature to several tens of thousands of degrees, accompanied by the ionization of hydrogen and helium. This part of the atmosphere is called chromosphere.

In the upper layers of the chromosphere, the density of the substance reaches 10 -15 g/cm 3 .

1 cm 3 of these layers of the chromosphere contains about 10 9 atoms, but the temperature increases to a million degrees. This is where the outermost part of the Sun's atmosphere, called the solar corona, begins.

The reason for the heating of the outermost layers of the solar atmosphere is the energy of acoustic waves arising in the photosphere. As they propagate upward into lower-density layers, these waves increase their amplitude to several kilometers and turn into shock waves. As a result of the occurrence of shock waves, wave dissipation occurs, which increases the chaotic velocities of particle movement and an increase in temperature occurs.

The integral brightness of the chromosphere is hundreds of times less than the brightness of the photosphere. Therefore, to observe the chromosphere, it is necessary to use special methods that make it possible to isolate its weak radiation from the powerful flux of photospheric radiation.

The most convenient methods are observations during eclipses.

The length of the chromosphere is 12 - 15,000 km.

When studying photographs of the chromosphere, inhomogeneities are visible, the smallest ones are called spicules. The spicules are oblong in shape, elongated in the radial direction. Their length is several thousand km, thickness is about 1,000 km. At speeds of several tens of km/s, spicules rise from the chromosphere into the corona and dissolve in it. Through spicules, the substance of the chromosphere is exchanged with the overlying corona. Spicules form a larger structure, called a chromospheric network, generated by wave motions caused by much larger and deeper elements of the subphotospheric convective zone than granules.

Crown has very low brightness, so it can only be observed during the total phase of solar eclipses. Outside of eclipses, it is observed using coronagraphs. The crown does not have sharp outlines and has an irregular shape that changes greatly over time.

The brightest part of the corona, removed from the limb no more than 0.2 - 0.3 radii of the Sun, is usually called the inner corona, and the remaining, very extended part is called the outer corona.

An important feature of the crown is its radiant structure. The rays come in different lengths, up to a dozen or more solar radii.

The inner crown is rich in structural formations resembling arcs, helmets, and individual clouds.

Corona radiation is scattered light from the photosphere. This light is highly polarized. Such polarization can only be caused by free electrons.

1 cm 3 of corona matter contains about 10 8 free electrons. The appearance of such a number of free electrons must be caused by ionization. This means that 1 cm 3 of the corona contains about 10 8 ions. The total concentration of the substance should be 2 . 10 8 .

The solar corona is a rarefied plasma with a temperature of about a million Kelvin. A consequence of high temperature is the large extent of the corona. The length of the corona is hundreds of times greater than the thickness of the photosphere and amounts to hundreds of thousands of kilometers.

18. Internal structure of the Sun.

Internal structure of the Sun

What is visible on the Sun?

Everyone probably knows that you cannot look at the Sun with the naked eye, much less through a telescope without special, very dark filters or other devices that attenuate the light. By neglecting this prohibition, the observer risks getting severe eye burns. The easiest way to view the Sun is to project its image onto a white screen. Using even a small amateur telescope, you can get a magnified image of the solar disk. What can you see in this image? First of all, the sharpness of the sunny edge attracts attention. The sun is a gas ball that does not have a clear boundary, its density decreases gradually. Why, then, do we see it sharply outlined? The fact is that almost all visible radiation from the Sun comes from a very thin layer, which has a special name - the photosphere. (Greek: “sphere of light”). The thickness of the photosphere does not exceed 300 km. It is this thin luminous layer that creates the illusion for the observer that the Sun has a “surface”.

Internal structure of the Sun

Photosphere

The atmosphere of the Sun begins 200-300 km deeper than the visible edge of the solar disk. These deepest layers of the atmosphere are called the photosphere. Since their thickness is no more than one three-thousandth of the solar radius, the photosphere is sometimes conventionally called the surface of the Sun. The density of gases in the photosphere is approximately the same as in the Earth's stratosphere, and hundreds of times less than at the Earth's surface. The temperature of the photosphere decreases from 8000 K at a depth of 300 km to 4000 K in the uppermost layers. The temperature of the middle layer, the radiation of which we perceive, about 6000 K. Under such conditions, almost all gas molecules disintegrate into individual atoms. Only in the uppermost layers of the photosphere are relatively few simple molecules and radicals of the type H, OH, and CH preserved. A special role in the solar atmosphere is played by a substance not found in terrestrial nature. negative hydrogen ion, which is a proton with two electrons. This unusual compound occurs in the thin outer, “coldest” layer of the photosphere when negatively charged free electrons, which are supplied by easily ionized atoms of calcium, sodium, magnesium, iron and other metals, “stick” to neutral hydrogen atoms. When generated, negative hydrogen ions emit most of the visible light. The ions greedily absorb this same light, which is why the opacity of the atmosphere quickly increases with depth. Therefore, the visible edge of the Sun seems very sharp to us.

In a telescope with high magnification, you can observe subtle details of the photosphere: it all seems strewn with small bright grains - granules, separated by a network of narrow dark paths. Granulation is the result of the mixing of warmer gas flows rising and colder ones descending. The temperature difference between them in the outer layers is relatively small (200-300 K), but deeper, in the convective zone, it is greater, and mixing occurs much more intensely. Convection in the outer layers of the Sun plays a huge role in determining the overall structure of the atmosphere. Ultimately, it is convection, as a result of a complex interaction with solar magnetic fields, that is the cause of all the diverse manifestations of solar activity. Magnetic fields are involved in all processes on the Sun. At times, concentrated magnetic fields arise in a small region of the solar atmosphere, several thousand times stronger than on Earth. Ionized plasma is a good conductor; it cannot move across the magnetic induction lines of a strong magnetic field. Therefore, in such places, the mixing and rise of hot gases from below is inhibited, and a dark area appears - a sunspot. Against the background of the dazzling photosphere, it appears completely black, although in reality its brightness is only ten times weaker. Over time, the size and shape of the spots change greatly. Having appeared in the form of a barely noticeable point - a pore, the spot gradually increases its size to several tens of thousands of kilometers. Large spots, as a rule, consist of a dark part (core) and a less dark part - penumbra, the structure of which gives the spot the appearance of a vortex. The spots are surrounded by brighter areas of the photosphere, called faculae or flare fields. The photosphere gradually passes into the more rarefied outer layers of the solar atmosphere - the chromosphere and corona.

Chromosphere

Above the photosphere is the chromosphere, a heterogeneous layer in which the temperature ranges from 6,000 to 20,000 K. The chromosphere (Greek for “sphere of color”) is so named for its reddish-violet color. It is visible during total solar eclipses as a ragged bright ring around the black disk of the Moon, which has just eclipsed the Sun. The chromosphere is very heterogeneous and consists mainly of elongated elongated tongues (spicules), giving it the appearance of burning grass. The temperature of these chromospheric jets is two to three times higher than in the photosphere, and the density is hundreds of thousands of times less. The total length of the chromosphere is 10-15 thousand kilometers. The increase in temperature in the chromosphere is explained by the propagation of waves and magnetic fields penetrating into it from the convective zone. The substance heats up in much the same way as if it were in a giant microwave oven. The speed of thermal motion of particles increases, collisions between them become more frequent, and atoms lose their outer electrons: the substance becomes a hot ionized plasma. These same physical processes also maintain the unusually high temperature of the outermost layers of the solar atmosphere, which are located above the chromosphere.

Often during eclipses (and with the help of special spectral instruments - and without waiting for eclipses) above the surface of the Sun one can observe bizarrely shaped “fountains”, “clouds”, “funnels”, “bushes”, “arches” and other brightly luminous formations from the chromospheric substances. They can be stationary or slowly changing, surrounded by smooth curved jets that flow into or out of the chromosphere, rising tens and hundreds of thousands of kilometers. These are the most ambitious formations of the solar atmosphere -. When observed in the red spectral line emitted by hydrogen atoms, they appear against the background of the solar disk as dark, long and curved filaments. Prominences have approximately the same density and temperature as the chromosphere. But they are above it and surrounded by higher, highly rarefied upper layers of the solar atmosphere. Prominences do not fall into the chromosphere because their matter is supported by the magnetic fields of active regions of the Sun. For the first time, the spectrum of a prominence outside an eclipse was observed by the French astronomer Pierre Jansen and his English colleague Joseph Lockyer in 1868. The spectroscope slit is positioned so that it intersects the edge of the Sun, and if a prominence is located near it, then its radiation spectrum can be seen. By directing the slit at different parts of the prominence or chromosphere, it is possible to study them in parts. The spectrum of prominences, like the chromosphere, consists of bright lines, mainly hydrogen, helium and calcium. Emission lines from other chemical elements are also present, but they are much weaker. Some prominences, having remained for a long time without noticeable changes, suddenly seem to explode, and their matter is thrown into interplanetary space at a speed of hundreds of kilometers per second. The appearance of the chromosphere also changes frequently, indicating the continuous movement of its constituent gases. Sometimes something similar to explosions occurs in very small areas of the Sun's atmosphere. These are the so-called chromospheric flares. They usually last several tens of minutes. During flares in the spectral lines of hydrogen, helium, ionized calcium and some other elements, the glow of a separate section of the chromosphere suddenly increases tens of times. Ultraviolet and X-ray radiation increases especially strongly: sometimes its power is several times higher than the total power of solar radiation in this short-wavelength region of the spectrum before the flare. Spots, torches, prominences, chromospheric flares - all these are manifestations of solar activity. With increasing activity, the number of these formations on the Sun increases.