List of brightest stars

More than 200 billion stars

The space is huge, our Milky Way galaxy contains over 200 billion stars distributed in a volume of 100 000 light-years in diameter. But to the naked eye, we see in the night sky that 9000 stars on a clear night, away from cities and flare the earth's surface.
The brightest stars are ranked by their average apparent magnitudes in the spectrum of visible light, seen from Earth.
Visible light is only a small range of electromagnetic vibrations found in the electromagnetic spectrum.
The light has a wavelength, which determines the color, for example red emitting in the wavelength of 700 nanometers, Orange 650 nm, Yellow 600 nm, Green 550 nm, Blue 500 nm and Violet 450 nm. It is this window that chose the human eye to specialize. But the invisible light is spread over a larger electromagnetic field.
The apparent magnitude does not indicate the intrinsic brightness of the star, in contrast to the absolute magnitude The absolute magnitude indicates the actual brightness of a celestial object, while the apparent magnitude depends on the distance of the object. The absolute magnitude of a star is defined as the apparent magnitude the star would have a distance of reference of 10 parsecs (≈32.6 light years) and in the absence of interstellar extinction (dustless between the object and the observer). A gain with a magnitude, corresponds to 2.5 times less brilliance. Example: the magnitude 1 of an object, is 2.5 times less bright than magnitude 2. . The apparent magnitude The brightness measured from Earth of a star or other celestial object is expressed in apparent magnitude. The magnitude scale is logarithmic and reversed, that is to say, the lowest magnitudes correspond to the brightest objects. A gain with a magnitude, corresponds to 2.5 times less brilliance. Example: the magnitude 1 of an object, is 2.5 times less bright than magnitude 2.  of course depends on the intrinsic brightness of the star but especially the distance from the Earth because the closest stars appear brighter.
Most stars are part of a binary or multiple system. Seen from Earth, they appear as a single star with an apparent magnitude greater than their individual brilliance.
The binary system of Rigel Kentaurus componed the star α Centauri A and star α Centauri B, the apparent magnitude of the couple is -0.27 while the apparent magnitude of α Centauri A is +0.01 and apparent magnitude of α Centauri B is +1.34, the couple is more brilliant, that's why it is ranked third after the Sun, in the table against.
Sirius is the brightest star in the night sky, but Sirius is a binary system, with the naked eye, we see only a single white star.
Sirius A is actually a white star, aged about 250 million years, with a mass of 2.1 solar masses, its surface temperature of about 9900 K and its diameter about 1.7 times the solar diameter. its companion, Sirius B is a white dwarf, i.e. a residue of star extinguished. This is the penultimate stage of the evolution of stars whose mass is between 0.3 and 1.4 times that of the sun. Sirius B orbits the center of mass of the pair, with a period of nearly 50 years. The distance between the two stars varies between 8.1 and 31.5 astronomical units (average distance 19.5 AU).

Table: list of the brightest stars in the order of their average apparent magnitude. For comparison, here are the maximum apparent magnitudes of the objects in our solar system: Moon (-12.92), Venus (-4.89), Jupiter (-2.94), Mars (-2.91), Mercury (-2.45) and Saturn (-0.49). To understand the colors of stars. see stars categories.

Image: Alpha Canis Majoris. The brightest star in the night sky after the Sun, is the white star Sirius (α CMa) located only 8.5 light-years away in the constellation Canis Major with Wezen and Adhara, other stars among the brightest.

Table: equivalences between the distance units (parsec, light year, astronomical unit and km).

What is a light year?
A light year is ≈10 000 billion km. This distance seems very high but the Oort cloud This remote and invisible region of the Solar System is located at 7500 billion km. It hosts billions of light icy body, to the limit of the attraction of the Sun can be disturbed by the slightest gravitational force, of the nearest stars of the solar system., a region of the solar system, is located at ≈7500 billion km and contains billions of icy bodies at the edge of the attraction of the Sun.