2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
One of the largest active regions this year has appeared on the disk of the Sun, which means that there are spots on the Sun again - despite the fact that our star is entering a period of minimum activity. Sergei Bogachev, Doctor of Physical and Mathematical Sciences, an employee of the Laboratory of X-ray Astronomy of the Sun of FIAN, tells about the nature and history of the detection of sunspots, as well as their effect on the earth's atmosphere.
In the first decade of the 17th century, the Italian scientist Galileo Galilei and the German astronomer and mechanic Christoph Scheiner, approximately simultaneously and independently of each other, improved the spyglass (or telescope) invented several years earlier and created on its basis a helioscope - a device that allows you to observe the Sun by projecting his image on the wall. In these images, they discovered details that could be mistaken for wall defects, if they did not move with the image - small spots dotting the surface of the ideal (and partly divine) central celestial body - the Sun. This is how sunspots entered the history of science, and the saying that there is nothing perfect in the world is in our life: "And there are sunspots on the Sun."
Sunspots are the main feature that can be seen on the surface of our star without the use of sophisticated astronomical techniques. The visible dimensions of the spots are on the order of one arc minute (the size of a 10-kopeck coin from a distance of 30 meters), which is at the limit of the resolution of the human eye. However, a very simple optical device, magnifying only a few times, is enough for these objects to be detected, which, in fact, happened in Europe at the beginning of the 17th century. Individual observations of spots, however, regularly occurred before that, and often they were made simply with the eye, but remained unnoticed or misunderstood.
For some time they tried to explain the nature of the spots without affecting the ideality of the Sun, for example, like clouds in the solar atmosphere, but it quickly became clear that they relate mediocrely to the solar surface. Their nature, however, remained a mystery until the first half of the 20th century, when magnetic fields were first discovered on the Sun and it turned out that the places of their concentration coincide with the places of formation of spots.
Why do the spots look dark? First of all, it should be noted that their darkness is not absolute. Rather, it is similar to the dark silhouette of a person standing against the background of an illuminated window, that is, it is only apparent against the background of a very bright ambient light. If you measure the "brightness" of the spot, you can find that it also emits light, but only at the level of 20-40 percent of the normal light of the Sun. This fact is enough to determine the spot temperature without any additional measurements, since the thermal radiation flux from the Sun is uniquely related to its temperature through the Stefan-Boltzmann law (the radiation flux is proportional to the temperature of the radiating body to the fourth power). If we put the brightness of an ordinary surface of the Sun with a temperature of about 6000 degrees Celsius as a unit, then the temperature of sunspots should be about 4000-4500 degrees. As a matter of fact, this is the way it is - sunspots (and this was later confirmed by other methods, for example, spectroscopic studies of radiation), are simply portions of the Sun's surface of a lower temperature.
The connection of spots with magnetic fields is explained by the influence of the magnetic field on the gas temperature. This influence is associated with the presence of a convective (boiling) zone in the Sun, which extends from the surface to a depth of about a third of the solar radius. The boiling of solar plasma continuously raises hot plasma from its interior to the surface and thereby increases the surface temperature. In areas where the surface of the Sun is pierced by tubes of a strong magnetic field, the efficiency of convection is suppressed until it stops completely. As a result, without being fed by hot convective plasma, the surface of the Sun cools down to temperatures of the order of 4000 degrees. A stain is forming.
Active area in the Sun April 26, 2018
Today spots are studied mainly as centers of active solar regions, in which solar flares are concentrated. The fact is that the magnetic field, the "source" of which are spots, brings additional reserves of energy into the Sun's atmosphere, which are "unnecessary" for the Sun, and it, like any physical system that seeks to minimize its energy, tries to get rid of them. This additional energy is called free energy. There are two main mechanisms for dumping excess energy.
The first is when the Sun simply throws out into interplanetary space the part of the atmosphere that burdens it, along with excess magnetic fields, plasma and currents. These phenomena are called coronal mass ejections. The corresponding emissions, spreading from the Sun, sometimes reach colossal dimensions of several million kilometers and are, in particular, the main cause of magnetic storms - the impact of such a plasma clot on the Earth's magnetic field unbalances it, makes it vibrate, and also increases the electric currents flowing in the Earth's magnetosphere, which is the essence of the magnetic storm.
The second way is solar flares. In this case, free energy is burned directly in the solar atmosphere, but the consequences of this can also reach the Earth - in the form of streams of hard radiation and charged particles. Such an impact, which is radiation in nature, is one of the main reasons for the failure of spacecraft, as well as auroras.
However, having discovered a spot on the Sun, you should not immediately prepare for solar flares and magnetic storms. A situation is quite common when the appearance of sunspots on the Sun's disk, even record-breaking large ones, does not lead to even a minimal increase in the level of solar activity. Why is this happening? This is due to the nature of the release of magnetic energy on the Sun. Such energy cannot be released from one magnetic flux, just as a magnet lying on a table, no matter how shaken it may be, will not create any solar flare. There should be at least two such streams, and they should be able to interact with each other.
Since one magnetic tube, piercing the surface of the Sun in two places, creates two spots, then all groups of spots in which there are only two or one spots are not capable of creating flares. These groups are formed by one thread, which has nothing to interact with. Such a pair of spots can be gigantic and exist on the disk of the Sun for months, frightening the Earth with its size, but will not create a single, even minimal, flare. Such groups have a classification and are called type Alpha, if there is one spot, or Beta, if there are two.
A complex sunspot of the Beta-Gamma-Delta type. Above - a spot in the visible range, below - magnetic fields shown by the HMI instrument on board the SDO space observatory
If you find a message about the appearance of a new spot on the Sun, do not be lazy and look at the type of group. If this is Alpha or Beta, then you can not worry - the Sun will not produce any flares or magnetic storms in the coming days. A more complex class is Gamma. These are groups of sunspots in which there are several sunspots of north and south polarity. In such a region, there are at least two interacting magnetic fluxes. Accordingly, such an area will lose magnetic energy and fuel solar activity. And finally, the last class is Beta Gamma. These are the most difficult areas, with an extremely confusing magnetic field. If such a group appeared in the catalog, there is no doubt that the Sun will unravel this system for at least several days, burning energy in the form of flares, including large ones, and ejecting plasma, until it simplifies this system to a simple Alpha or Beta configuration.
However, despite the "frightening" connection of spots with flares and magnetic storms, one should not forget that this is one of the most remarkable astronomical phenomena that can be observed from the surface of the Earth in amateur instruments. Finally, sunspots are a very beautiful object - just look at their high-resolution images. Those who, even after that, are not able to forget about the negative aspects of this phenomenon, can be comforted by the fact that the number of spots on the Sun is still relatively small (no more than 1 percent of the disk surface, and often much less).