May 17, 2022

The Sun (from Latin: Sol) is the mother star of the solar system, around which the eight main planets (including the Earth), the dwarf planets, their satellites, countless other minor bodies and the dust scattered through space orbit , which forms the interplanetary medium. The mass of the Sun, which amounts to about 2 × 1030 kg, alone represents 99.86% of the total mass of the solar system. mass, 92.1% of its volume) and helium (about 24-25% of the mass, 7.8% of the volume), to which are added other heavier elements present in traces. It is classified as a "yellow dwarf "of spectral type G2 V:" G2 "indicates that the star has a surface temperature of 5777 K (5504 ° C), a characteristic that gives it an extremely intense and chromatically cold white color which, however, can often appear yellowish due to light scattering in the earth's atmosphere, due to the elevation of the star above the horizon and, nevertheless, to the atmospheric clarity. The V (5 in Roman numerals) indicates that the Sun, like most of the stars, is in the main sequence, that is, in a long phase of stable equilibrium in which the star merges hydrogen into helium in its core. This process generates a large amount of energy every second (equivalent to a power of 3.9 × 1026 W), emitted into space in the form of electromagnetic radiation (solar radiation), flux of particles (solar wind) and neutrinos. Solar radiation, basically emitted as visible and infrared light, allows life on Earth by supplying the energy necessary to activate the main mechanisms underlying it; moreover, the insolation of the earth's surface regulates the climate and most of the meteorological phenomena. Located within the Orion Arm, a secondary arm of the galactic spiral, the Sun orbits the center of the Milky Way at an average distance of about 26,000 light years and completes its revolution in 225-250 million years. Among the closest stars, placed within a radius of 17 light years, the Sun is the fifth brightest in intrinsic terms: its absolute magnitude, in fact, is equal to +4.83. If it were possible to observe our star from α Centauri, the closest star system, it would appear in the constellation of Cassiopeia with an apparent magnitude of 0.5.The symbol of the Sun consists of a circle with a point in the center (Unicode: U + 2609 ; entity in HTML, XML and derivatives languages: ☉ ☉).


The Sun is the only star whose shape can be appreciated simply by sight, thanks to its average apparent angular diameter of 32 '03 "of arc, which however varies according to where the Earth is during its orbit: in fact it reaches the maximum value (32 '35 ") when our planet is at perihelion, while the minimum value (31' 31") at the aphelion. Similar apparent dimensions allow, subject to the use of particular instruments and adequate protections, to observe the details of the surface of our star in order to reveal and study the phenomena that characterize it. With the naked eye it is possible to distinguish the solar disc at sunset or in the presence of fog and clouds, when the light intensity is significantly lower. These observations allow, albeit in rare circumstances, to observe particularly large sunspots. Using a modest telescope, equipped with a suitable filter or used to project the image of the star on a white screen, it is possible to easily observe sunspots and flares. However, due to the risks to which the retina of the eye is subject, observing the Sun without the right protections is harmful to sight: in fact, the strong radiation can cause the death of part of the eyes.