The star brightness perceived by eyes of the person in astronomy is called visible star size. Also there is a parameter of luminosity of a celestial body which size does not depend on distance between the observer and a star.
What star brightness depends on
For the first time on brightness the Ancient Greek astronomer Gipparkh began to distinguish stars in the 2nd century BC. He allocated 6 degrees in a luminescence and entered a concept of star size. The German astronomer Johann Bayer at the beginning of the 17th century entered designation of brightness of stars in constellations letters of the Greek alphabet. The brightest stars for a human eye received the name α such constellation, β – the following on brightness, etc.
The is hotter a star, the more light it radiates.
Blue stars have the biggest luminosity. Less bright white. Yellow stars have the average size of luminosity, and red giants are considered as the most dim. The luminosity of a celestial body is a changeable size. For example, in the chronicle dated on July 4, 1054 it is told about a star in the constellation of the Taurus so bright that it it was visible even in the afternoon. Over time the star began to grow dull, and in its year it was already impossible to see with the naked eye. Now in the constellation of the Taurus it is possible to observe the Crab Nebula – a trace after explosion of a supernova. In the center of a fog the astronomers found a source of a powerful radio emission – a pulsar. All this that remained supernew from explosion, observed in 1054.
The brightest stars in the sky
The brightest stars in the Northern hemisphere are the Deneb from the Cygnus constellation and Riegel from the constellation of Orion. Their luminosity exceeds luminosity of the Sun in 72500 and 55000 times respectively. They are at distance of 1600 and 820 light years from Earth. One more bright star of the Northern hemisphere - Betelgeuse - is also located in the constellation of Orion. It radiates in 22000 times more of light, than the Sun.
Most of all bright stars in the Northern hemisphere it is possible to observe in the constellation of Orion.
Sirius from the constellation of the Big Dog is the brightest star seen from Earth. It can be observed in the Southern hemisphere. Sirius is brighter than the Sun only by 22.5 times, but the distance to this star to space measures is small – 8.6 light years. The pole star in the constellation of Little Dipper shines as 6000 Sun, but it is removed from us on 780 light years therefore looks more dim than close Sirius. In the constellation of the Taurus the star with the astronomical name UW SMa is located. It is possible to see it only in the telescope. The blue star differs in the huge density and small spherical size. It shines 860000 times brighter than the Sun. This unique celestial body is considered the brightest object in an observed part of the Universe.