What is a Star?
What is a Star?
Stars Sirius A (left) and Sirius B (right).A star is a sphere of gas in a state of equilibrium between gravity, which tends to compress it, and the pressure of the gas, which tends to expand. The stars generate energy in their interior through thermonuclear reactions. The energy generated is emitted into space in the form of electromagnetic radiation (light), neutrinos ("exotic" particles) and stellar wind (gas).
The stars are observed in the night sky as luminous points, twinkling due to the optical distortions produced by the turbulence and the density differences of the terrestrial atmosphere.View of stars as luminous points from Valley of the Cochiguaz in the
fourth region of Coquimbo, Chile.
Image credits: Hernán Stockebrand.
The Sun is a star that being so close is not observed as a point, but as a luminous disk whose presence or absence in the terrestrial sky causes day or night respectively.Cooler stars may have surface temperatures of approximately 2000 ° C, while the hottest ones may reach around 50000 ° C. There are some stars in very advanced stages of your life that can be even hotter. The Sun has a temperature on its surface (the disk we observe) of 6000 ºC and its core reaches 15 million degrees.The Sun, our nearest star, located at 150000000 km of Earth.The atomic nuclei of all the chemical elements that we know have been created inside the stars from the "fusion" of simpler nuclei, beginning with the "fusion" of hydrogen.The nucleosynthesis It is the origin of the energy of the stars, since the formation of elements lighter than iron releases energy. The mass of the products of the fusion is smaller than the mass of the fused nuclei and the difference is transformed into energy (E = mc2) and constitutes the source of the radiation that we receive from the stars. This radiation is originated in the core of the star and is transported to the outer layers suffering in its journey numerous absorptions and re-emissions by the stellar material. The layer of the star where the last re-emission of visible light occurs is the photosphere.
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