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Stars are masses of gases, mainly hydrogen and helium, that emit light. They are at very high temperatures. Inside there are nuclear reactions.
The Sun is a star that we have very, very close. We see the other stars as very small luminous points, and only at night, because they are at great distances from us.
They seem to be fixed, always maintaining the same relative position in the heavens, year after year. But it's not like that; in reality, all these stars are in rapid motion, although at distances so great that their position changes are perceived only through the centuries.
The number of stars observable to the naked eye from Earth has been estimated at about 8,000, half in each hemisphere. During the night you can not see more than 2,000 at the same time, the rest are hidden by the atmospheric fog, especially near the horizon, and the pale light of the sky.
Astronomers have calculated that the number of stars in the Milky Way, the galaxy to which the Sun belongs, amounts to hundreds of billions.
Like our Sun, a typical star has a visible surface called photosphere, an atmosphere full of hot gases and, above them, a more diffuse crown and a stream of particles called stellar wind. The coldest areas of the photosphere, than in Sun They are called sunspots, they are probably found in other common stars. This has been proven in some large nearby stars by interferometry.
The internal structure of the stars cannot be observed directly, but there are studies that indicate convection currents and a density and temperature that increase until reaching the nucleus, where thermonuclear reactions take place.
The stars are composed mostly of hydrogen and helium, with varying amounts of heavier elements.
The closest star to the Solar System is Alfa Centauro
The individual stars visible in the sky are those closest to the Solar System in the Milky Way, our galaxy. The closest is Proxima Centauri, one of the components of the triple star Alpha Centauri, which is about 40 billion kilometers from Earth.
It is a three-star system located 4.3 light years from the earth, which is only visible from the southern hemisphere. The brightest, known as "Alpha Centaur A" has a real brightness equal to that of our Sun.
Alpha Centauri, also called Rigil Kentaurus, is in the constellation of Centaur. At first glance, Alfa Centauro appears as a single star, with an apparent magnitude of -0.3, which makes it the third brightest star in the sky visible from the southern hemisphere.
When viewed through a telescope, it is noted that the two brightest stars, Alpha Centauri A and B, have apparent magnitudes of -0.01 and 1.33 and revolve around each other over a period of 80 years.
The weakest star, Alpha Centauri C, has an apparent magnitude of 11.05 and revolves around its companions for a period of approximately one million years. Alpha Centauri C is also called Proxima Centauri, as it is the closest star to the Solar system.
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