Sunspots – how do they form and what do they tell us about the sun’s activity?

As early as the 5th century BC, Chinese observers noticed it. We learned this in the middle of the nineteenth century Their number and location are subject to periodic changes, the duration of which is about 11 years. In the 20th century, scientists concluded that their occurrence was related to magnetic vortices in the solar atmosphere. we talk about spots on the sun – a phenomenon as wonderful as it is mysterious.

A sunspot is just a dark region in the photosphere of the solar system’s central star. These structures often appear in clusters, and the largest can measure more than 50,000 meters in diameter. how much. They look almost black and exist for a short time (from a few hours to several months). At this point, it should be emphasized that their black color is actually an optical illusion caused by the difference in temperature of sunspots and other regions of the sun.

Sunspots have a temperature of about 4000-5000 K, so they are very hot. Why do areas look black? It’s simple – contrast with a much hotter environment, about 6,000 K, and the radiation intensity changes with the fourth power of temperature.

It is worth noting that the periodic occurrence of sunspots is not unique to the Sun. Other stars like it, especially red dwarfs, exhibit periodic changes in brightness. Like the central star, they also have their own stars star spotsas a result of similar operations.

to grow up spots on the sun It corresponds to the phenomenon of differential rotation. We are talking about different angular velocities of different parts of the subsurface layer (i.e. convection) of the Sun. At the equator, the orbital period is 25 days, but around 45° latitude the rate of rotation slows and the orbital period increases to 27.6 days. In contrast, in the region of the poles, the rotation rate is lowest, and the orbital period is 30.8 days.

As a result of the occurrence of differential spin, a mechanism is created to generate a magnetic field at the expense of the kinetic energy of the plasma. In the boundary region of the photosphere and atmosphere, the energy of the plasma is lower than that of the magnetic fields. This leads to an increase in solar activity, which is manifested, among other things, in the occurrence of sunspots.

In other words, the formation of sunspots is caused by a strong magnetic field (the flux is characterized by an induction of 0.4 Tesla), which limits the phenomenon of convection. The hot plasma does not rise into the atmosphere, so the surface of the photosphere cools and collapses (spots on the Sun lie about 1,000 km below its circumference).

number spots on the sun It provides scientists with a measure of the activity of the solar system’s central star. When the spots are the most, it must be assumed that the sun is in the middle of the cycle.

Currently, our star is in the twenty-fifth cycle. The peak phase of activity will come in 2025, in July to be exact. Researchers are convinced that about 115 spots will be visible on the Sun.

It may seem that the more sunspots there are on the surface of the Sun, the lower the temperature on Earth. In practice, the opposite is true, because as the number of sunspots increases, the central star radiates more energy. How is this possible, since the temperature of sunspots is much lower than that of the surrounding photosphere?

Sunspots are almost always accompanied by other forms of solar activity, including so-called solar flares. Under this name are regions hotter than the average temperature of the photosphere (by about 300 K). As a result, the increased flares compensate for the lower radiation emission that occurs in the sunspot region.

Confirmation of this may be the fact that during periods of minimum solar activity, during which there are no sunspots on the Sun, the temperature drops. This was the case between 1790 and 1830, when the Dalton Minimum occurred. Then the lack of sunspots became one of the factors that led to the occurrence of the so-called Little Ice Age in the Old Continent.

However, this does not mean that a decrease in solar activity will lead to a global cooling of the climate. According to the researchers, even if a solar minimum comparable to the Dalton Minimum occurred this century, the decreased activity could lead to a cooling of 0.1 to 0.3 degrees Celsius. Meanwhile, strengthening the greenhouse effect, resulting from increased production of greenhouse gases, would cause the temperature to increase by about 2.4 degrees Celsius. With these estimates in mind, we must conclude that solar activity affects Earth’s climate to a lesser extent than human activity.

The earliest mention of sunspots dates back to the 5th century BC, and at that time, Chinese observers noticed dark areas on the surface of the sun. Sandstorms have created favorable observation conditions for them. In the years 1610-1620, several astronomers spotted spots on the Sun – Galileo, Thomas Harriot, Johannes, David Fabricius, Christoph Scheiner. The spots seen through a telescope were the oldest, in 1611, described by Johannes Fabricius.

The index of solar activity, based on the number of sunspots on the Sun, was made already in the middle of the 19th century, based on the wolf number. Johann Rudolf Wolf defined the R number of sunspots as the sum of the number of sunspot groups (active areas) multiplied by ten and sunspots (W = 10 * g + f, where g is the number of active areas, af – the number of sunspots).

Wolf extended his calculations with historical data, the result of 150 years of observations. So he had to take into account in his work the different powers of the telescopes used. In order to correct for possible differences, he introduced a scale factor k, which was determined separately for each observer. For his observations, he used a k-factor of 1. This value increased for observers using telescopes and older portable devices. In order to recreate as accurately as possible the conditions in which his predecessors worked, he did not include in his calculations the smallest points that did not have a penumbra, and calculated points with a common penumbra in the sum.

After Wolf’s death, Alfred Wolfer undertook to update the sunspot index. In his calculations, he included points without a pen, but to bring the results closer to the Wolff series, he used a k-factor of 0.6. In the middle of the twentieth century, the methodology for calculating the indicator was updated again. At that time, he also began to take sunspot size into account.

In 1980, the Wolf Number was renamed the International Relativistic Sunspot Number (Ri). For its calculation, data recorded by observatories around the world were used (data were previously collected in Zurich), normalized to values ​​from the reference station in Locarno.