A star is a object similar to our sun, which shines through nuclear reactions that occur in the center.
With the exception of the Sun, the stars appear to the naked eye as a bright, glittering due to atmospheric turbulence, without immediate apparent motion relative to other fixed objects in the sky.
All the stars are considerably more distant from Earth than Sun.
The nearest star, Proxima Centauri, is located about 4 light years of the solar system, nearly 250 000 times farther than the Sun.
The mass of a star is the order of 1030 kg and its radius of about a few million miles.
The power radiated by a star like the Sun is about 1026 watts. Stars form due to the contraction of a nebula of gas and dust under the influence of gravity.
If the heating of the material is sufficient, it will trigger the cycle of nuclear reactions in the heart of the nebula to form a star.
The energy released by these reactions is then sufficient to stop its contraction due to the radiation pressure generated.
The number of stars in the Universe is estimated between 1022 and 1023.
Apart from the Sun, the stars are too faint to be observable in daylight.
Image: Birth of a star image made from data of X-ray telescope Chandra (blue) and data from the Spitzer infrared telescope (red and orange). NB: The astronomers classify stars in dwarf or giant.
At about 4000 light years from Earth lies RCW 108, a region of the Milky Way, where star formation is active where the presence of clusters of young blue stars in the picture.
That we see born, yellow in the center of the image is deeply rooted in a cloud of molecular hydrogen.
The red dwarf are small red stars.
These stars among the smallest as white dwarfs, neutron stars and brown dwarfs do not consume nuclear fuel.
The mass of red dwarfs is between 0.08 and 0.8 solar masses. A surface temperature between 2500 and 5000 K gives them a red color.
Because of their small mass red dwarfs burn hydrogen slowly and they therefore have a very long lifespan, estimated at between tens and 1 000 billion years.
They contract and heat up slowly until all their hydrogen is consumed. Red dwarfs are probably the most numerous stars in the universe.
Proxima Centauri, the nearest star to us is a red dwarf, and some twenty of the thirty other nearby stars.
Image: Alpha Centauri, as the majority of stars is a red dwarf. NB: The astronomers classify stars in dwarf or giant.
It is the star closest to us, to 4.22 light years from our Sun, it is part of a triple star system (captured in the center of the image).
It is visible only through a telescope.
The brightest star in the Alpha Centauri system is quite similar to our Sun.