A supernova is the visible phenomenon, directly stemming from the disastrous explosion of a star which ends in its total destruction and thus in the death of the star.
This explosion comes along with a gigantic increase of its luminosity seen by the Earth, which can last until several weeks and even several months. It is visible in broad daylight and harms it, she can be also brilliant as the moon and even give a shade to objects.
A supernova often appears thus as a new star, where from its name, nova.
Supernovae are rare events in our Milky Way, approximately one-three by century, on the other hand on the scale of the universe, we observe it every day. It is during its explosion in supernova that the star frees the chemical elements that it synthetized during its existence and during the explosion itself.
The shock wave of the supernova facilitates the formation of new stars by accelerating the contraction of regions of gas and dusts of the interstellar middle. Novae, unlike supernovae arise from thermonuclear explosions which provoke a partial destruction of the star by expelling a part of its surface in the interstellar space. Our sun will not end its life in supernova but in a much more quiet way.
The death of a star can be sweet or rapes, it depends on its mass. | | Below 1,4 times the mass of the Sun, the star goes out in the serenity, it will pass of the size of a red giant (approximately 50 million Km of beam), in that of the Earth (approximately 6 000 km of beam). The star becomes then a white dwarf. Between 1,4 and 5 times the mass of the Sun, its agony is much more violent. Its beam narrows up to 10 km.
The final density is enormous, nuclei cannot resist and the heart of the star becomes a gigantic nucleus of neutrons.
The collapse provokes a terrible explosion which is going to throw the superior layers of the star in the space and we shall see shining in the sky, a supernova. Above 5 times the mass of the Sun, the collapse is extremely violent.
This one cannot be any more arrested. The heart of the star becomes a black hole.
The violence of the collapse produces a gigantic explosion which throws the superior layers of the star in the space. As in the previous case a supernova is going to extend over hundreds of billion Km, sowing the interstellar middle of heavy elements, made during the life of the star and during the explosion.
These heavy elements are the constituents of telluric planets as our Earth.  List of the supernovae
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 The most famous supernova of the history of the astronomy. SN 1054 is a supernova the explosion of which was seen since the Earth from July 4th, 1054, called misty of the crab today which is situated in our galaxy in the constellation of the bull.
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