There are two significantly different types of radiation from the Sun: electromagnetic wave radiation and particle emission.
Electromagnetic waves emitted by the Sun only partially reach the Earth's surface, the rest are absorbed (absorbed) by the atmosphere. The latter has two transparency windows: an optical window and a radio window. Through the optical window, radiation with a wavelength of 3000 to 10 000 A passes through - this is approximately the radiation that we perceive as visible light (1 A = 1 angstrom = 10-7 mm). In addition to the tangible thermal rays with wavelengths of up to 1 cm, the radio waves from 1 cm to 10 m are also part of the waves that reach the earth's surface. Radiation research on these waves is carried out by a whole branch of modern astronomy - radio astronomy, which is described in more detail below. Color sensations occur in the eye in response to the perception of light at different wavelengths. The color of the shortest waves (about 400 millionths of a millimeter) is purple; even shorter waves in the invisible part of the spectrum are called ultraviolet radiation. The feeling of red is caused in our eyes by the radiation of large wavelengths (about 800 millionths of a millimeter). Even longer wavelengths of radiation are called infrared or thermal; they are also invisible to us. Ultraviolet radiation is almost completely absorbed by the atmosphere. If the atmosphere were transparent to ultraviolet radiation, then life on Earth could not exist in the forms we know. Already in the small quantities in which we receive ultraviolet radiation, we sometimes feel the "harmful effect: with intense exposure to sunlight, its ultraviolet component affects our skin, causing the appearance of tanning.
Particle emission
Particle emission (corpuscular radiation) in contrast to electromagnetic radiation is the emission of the smallest particles of matter, fragments of hydrogen atoms, which fly away from the Sun at a speed of 100 to 2000 km/sec. They reach the upper layers of the Earth's atmosphere (ionosphere) and cause spectacular polar lights to appear at high altitudes. In addition to the polar lights, there is another phenomenon. Due to the physical changes in the atoms and molecules of the corresponding layers, occurring under the influence of strong ultraviolet radiation of the Sun, these layers become "transparent" for a time for short radio waves, i.e. they no longer reflect short radio waves sent from the Earth, and therefore make it impossible to communicate on short waves. Corpuscular and ultraviolet radiation, as well as the radiocommunication disruption they cause, become particularly strong when certain short-term processes, known as solar flares (eruptions), begin to occur in the Sun.
Solar activity phenomena
Solar activity is expressed in various phenomena. The most remarkable and known are sunspots. They can be observed with simple optical aids. Spots that appear to us to be dark spots or dark areas on the solar surface are areas with lower temperatures than the surrounding matter of the photosphere. They can be called gas whirlwinds of enormous proportions. They often appear in groups of up to 200,000 km in total, which is 15 times the diameter of the Earth. Spots in groups are not always equal in number and size. There are years in which the frequency of slicks is increased and decreased. It has been established that the abundance of slicks changes on average with an average period of 11 years. Every 11 years, slicks are large and numerous (maximum slicks); there are time intervals between these periods with reduced slicks frequency (minimum). Since outbreaks near sunspots produce particularly strong ultraviolet and corpuscular radiation, during the period of maximum sun spotting activity the polar lights and radio communication disturbances are particularly intensified. However, the predictions of astrologers, who attribute the maximum solar activity to the increased risk of war and epidemics, are erroneous; they have no scientific basis.
Torches, areas of increased brightness (particularly visible on the slightly darker edges of the solar disk), often appear as light veins in the vicinity of spots. These can be superheated areas of higher layers of the solar atmosphere with increased radiation.
Flashes are very powerful, short-lived phenomena, in most cases in or around large groups of spots. They emit powerful ultraviolet, X-ray and corpuscular radiation, which are responsible for the above-mentioned disturbances of the Earth's ionosphere and polar lights.
Protuberances are another expression of solar activity. Here we are dealing with hot gas clouds thrown out at high altitudes. They sometimes break far beyond the chromosphere and can reach heights of several hundred thousand kilometers. The frequency of protuberances and torches also changes with about 11 years of age. They can be observed not only with a complete solar eclipse but also with the help of special devices.
We are familiar with the movements of the sun as we see them, i.e. the seeming movements, from experience. The daily movement of the Sun from east to west is due, as has already been said, to the rotation of the Earth on its axis from west to east. Depending on the time of year, we see the Sun at noon, sometimes higher or lower above the horizon. This is a consequence of its annual motion. But even this movement only seems to be a reflection of the movement of the Earth around the Sun. In this case, the change in the height of the Sun above the horizon at noon during the year is a consequence of the parallelism of the Earth's axis itself in the space when the Earth revolves around the Sun.
When summer is summer in the northern hemisphere, the northern half of the globe is facing the Sun and the height of the Sun at noon is about 60° at this time. When we have winter, the southern hemisphere is facing the Sun and the Sun reaches a height of only 15°. Because of the different angles of incidence of radiation on the surface of the Earth in these two cases, there is different heating of the surface and the air to which the surface transmits heat. Thus, the change in seasons is not due to a change in the distance from the Earth to the Sun, but on the contrary, in the northern hemisphere, summer is just when the Earth is at its maximum distance from the Sun!
In addition to these visible movements, the Sun makes real movements. It rotates around its axis at a speed of one revolution in 27 days. In addition, along with all the bodies of the Solar System it moves among the stars at a speed of 20 km/sec towards the constellation of Hercules, and together with all the stars surrounding it takes part in the rotation around the center of the Milky Way at a speed of 200 km/sec.