Traditionally, the Sun is a source of light. However, light is only one of the forms through which the energy produced by the star is dispersed into space. Like all stars, the Sun also emits non-visible energy in the form of infrared and ultraviolet radiation, X-rays and radio waves, or as a flow of charged particles, called the "solar wind". However, not all this radiation reaches the Earth's surface: the atmosphere and the Earth's magnetic field act like an impenetrable shield to block this flow. And luckily so, because otherwise all forms of life on our planet would soon be wiped out. However, for astronomers, the problem is quite serious: from the Earth, they can see the Sun and the other stars, but they cannot completely analyze their behavior. To do so, they must leave the Earth's atmosphere, taking special instruments into orbit. This is exacly what Skylab did and, among other things, the spacecraft also carried instruments to measure the ultraviolet radiation and "x-rays" from the Sun. The results were amazing and created a great flurry of excitement in the scientific world. Space astronomers finally could observe the corona in all its regal majesty: a gigantic halo two times the size of the solar disk which is also divided into segments with varying temperatures, the hottest of which even reaches a million degrees Celsius. It was also discovered that the surface of the Sun is much more turbulent than ever imagined. The outermost gaseous shell, called the chromosphere, with a "thickness" that varies between 10 000 and 15 000 kilometers, is also the site of some very spectacular events: prominences, columns of incandescent gas which rise from the surface up to a height of 500 000 kilometers. There are many different types and their names indicate their various forms: wave, ring, arc, fan, bush ... These enormous red flames may develop very quickly, in just a few hours, or may even last several days before slowly weakening and fading away. But from Skylab it was also possible to observe the photosphere, the bright red gaseous envelope immediately below the chromosphere. With a thickness of only 320 kilometers (covering the entire solar mass like the skin of a gigantic peach), the non-homogeneous chromosphere seems to consist of many bright "grains" scattered over a darker bottom. Each grain has a very short life: it shines and disappears in just a few minutes because it is nothing but the end of the column of gas which, together with all the others, form the underlying area. The famous sunspots appear in the photosphere and finally they could be fully studied from space. Direct observation has confirmed that the sunspots are large depressions where matter is trapped by gigantic magnetic fields which are six thousand times more powerful than those found on the Earth. Sunspots often appear in complex groups, where immense filaments of incandescent gas are suddenly "shot" upwards and then fall back to the surface. These flares or spicules generate a flow of charged particles that hurtle into our atmosphere, disturbing radio transmissions, making compasses go crazy and creating the polar lights, fantastic faded patterns of luminous colors which appear and disappear in the arctic and antarctic nights.
Traditionally, the Sun is a source of light. However, light is only one of the forms through which the energy produced by the star is dispersed into space. Like all stars, the Sun also emits non-visible energy in the form of infrared and ultraviolet radiation, X-rays and radio waves, or as a flow of charged particles, called the "solar wind". However, not all this radiation reaches the Earth's surface: the atmosphere and the Earth's magnetic field act like an impenetrable shield to block this flow. And luckily so, because otherwise all forms of life on our planet would soon be wiped out. However, for astronomers, the problem is quite serious: from the Earth, they can see the Sun and the other stars, but they cannot completely analyze their behavior. To do so, they must leave the Earth's atmosphere, taking special instruments into orbit. This is exacly what Skylab did and, among other things, the spacecraft also carried instruments to measure the ultraviolet radiation and "x-rays" from the Sun. The results were amazing and created a great flurry of excitement in the scientific world. Space astronomers finally could observe the corona in all its regal majesty: a gigantic halo two times the size of the solar disk which is also divided into segments with varying temperatures, the hottest of which even reaches a million degrees Celsius. It was also discovered that the surface of the Sun is much more turbulent than ever imagined. The outermost gaseous shell, called the chromosphere, with a "thickness" that varies between 10 000 and 15 000 kilometers, is also the site of some very spectacular events: prominences, columns of incandescent gas which rise from the surface up to a height of 500 000 kilometers. There are many different types and their names indicate their various forms: wave, ring, arc, fan, bush ... These enormous red flames may develop very quickly, in just a few hours, or may even last several days before slowly weakening and fading away. But from Skylab it was also possible to observe the photosphere, the bright red gaseous envelope immediately below the chromosphere. With a thickness of only 320 kilometers (covering the entire solar mass like the skin of a gigantic peach), the non-homogeneous chromosphere seems to consist of many bright "grains" scattered over a darker bottom. Each grain has a very short life: it shines and disappears in just a few minutes because it is nothing but the end of the column of gas which, together with all the others, form the underlying area. The famous sunspots appear in the photosphere and finally they could be fully studied from space. Direct observation has confirmed that the sunspots are large depressions where matter is trapped by gigantic magnetic fields which are six thousand times more powerful than those found on the Earth. Sunspots often appear in complex groups, where immense filaments of incandescent gas are suddenly "shot" upwards and then fall back to the surface. These flares or spicules generate a flow of charged particles that hurtle into our atmosphere, disturbing radio transmissions, making compasses go crazy and creating the polar lights, fantastic faded patterns of luminous colors which appear and disappear in the arctic and antarctic nights.
