nightfalling

the sky full of stars

continuous spectrum

dark lines in the spectrum

description of the elements building the spectrum lines

the structure of the hydrogen atom

animation of the thermonuclear reactions

Stars have been accompanying a human since the dawn of his history. For ancients there were only the flickering points helping them to orientate in their area. For them the stars were the manifestations of the power of their gods living somewhere high in the sky and observing the human’s deeds. For the others they were the lights of the souls of their dead relatives and friends. But there was one group of people, for who the stars were the objects of studies and scientific considerations. Thanks to them - astronomers - we can make this wonderful stellar journey.

After adding a narrow slit and special optical system, the mysterious dark lines have been noticed in the sunlight spectrum. Each star, like the Sun, is the remote source of light. So for each star the spectrum can be studied. And thanks to this method, by studying the spectrum of the Sun and other stars we got more information about these objects. One of the most important discoveries was, that the spectrums of some stars are identical with the Sun spectrum.

It became clear, that the arrangement and number of dark lines in a spectrum are caused by the chemical composition and the temperature of the lighting gas, which builds the stars and the Sun. And that became the best method for studying the stars even if they are so distant.

Cooler external layers cause scattering of some parts of radiation and create characteristic for each star dark lines called the absorption lines. Compering the arrangement of these lines with the laboratory spectrum we can know the chemical composition of the stellar atmospheres and the same of our Sun.

And in this way it was found, that the Sun is a giant sphere built in three quarters of hydrogen and in one quarter of helium, the other elements make up just 1% of its mass.

The Sun is a star of average size, with almost 1,5 mln kilometres in diameter. Its inside would contain more than one million of the Earth’s spheres. The Sun only apparently seems to be a quiet star. Its surface is boiling with the temperature reaching 6000 degrees. And there are huge streams - protuberances being threw above it. Most of the matter falls back on the Sun’s surface, but part of it goes irretrievably in the Cosmos. Dark spots on the surface are the results of the Sun magnetic activity. They seem to be black, because they are colder then the surrounding atmosphere. But their temperature reaches 4000 degrees. Inside the Sun, where the energy is produced, the temperature rises up to 15 million degrees.

But what kind of processes cause such rise in temperature? It turned out that responsible for this are the smallest matter particles - elementary particles, and thermonuclear reactions.

The hydrogen atom is the essential building material in the Universe. It consists of positive nucleus and surrounding it - negative electron. Hydrogen is the Sun’s essential component. But when the sun temperature is so high hydrogen is not able to hold its electron on its orbit, that’s why the matter inside the Sun is the disordered mixture of nucleons and electrons.

The collision of two hydrogen nuclei (protons) causes the rise of hydrogen isotope. In this process the portion of energy and a small elementary particle are emitted. The collision with next proton gives another portion of energy and helium isotope. The collision of two such threes - it is the next portion of energy, abstraction of two protons, what gives the final product, which is the helium nucleus consisting of two protons and two electrons. In such way, in the Sun’s core, hydrogen is changed into helium with producing so great amount of energy, which results in sunshining. And so the smallest participles are responsible for shining of so great gas atmosphere - our Sun.

But such state has not been lasting for ever. Somehow these reactions started.

To find out how it happened we have to move back about 5 billion years.

There was a huge gas and dust cloud drifting through the space. Because of the gravitational disturbances, maybe it was close explosion of supernovae, part of this cloud started to contract. The cloud became smaller and more condensed. The temperature in its centre started to rise up and at last was so high that caused first thermonuclear reactions. Hydrogen started to be changed into helium and balanced the gravitational subsidence, and our Sun was born. This process took place 5 billion years ago. From that time the Sun is an average star quietly synthesising helium. And it will not change for next 5 billion years. Then the amount of hydrogen will be to small and the Sun, starting next thermonuclear reactions based on helium fuel - will became big, red and cold on its surface. Its inside will absorb our Earth, which orbit is too small to hold the central star. Such state will last for just one million years until the Sun throws away the external atmosphere layers and creates the spectacular, spreading out in the space, gas cloud - planetary nebula. Our Sun will become just a white dwarf - the burnt suncore, which will cool down in next billions of years until it finally disappears in the black Cosmos.