What determines the brightness of the stars
For the first time the stars the brightness began to distinguish in the II century BC the ancient Greek astronomer Hipparchus. He singled out 6-degree illumination and introduced the concept of magnitude. German astronomer Johann Bayer in the early seventeenth century introduced the symbol of the brightness of stars in constellations with Greek letters. The brightest to the human eye of the light received the name α such and such a constellation, β is the next in brightness, etc.
The hotter the star, the more light it emits.
The biggest luminosity have blue stars. Less bright white. The average value of the luminosity have yellow stars, and the dim are considered to be red giants. The luminosity of a celestial body is a fickle value. For example, in the chronicle, dated July 4, 1054, describes a star in the constellation Taurus, so bright that it was visible even during the day. Over time, the star began to fade, and after a year it was impossible to see with the naked eye.
Now in the constellation Taurus it is possible to observe the Crab nebula is the trace after the explosion of a supernova. In the centre of the nebula, astronomers have discovered the source of powerful radio emission of the pulsar. This is all that remains from a supernova explosion observed in 1054.
The brightest stars in the sky
The brightest stars in the Northern hemisphere are Deneb from the constellation Cygnus and Rigel in the constellation of Orion. Their luminosity exceeds the luminosity of the Sun 72500 and 55000 respectively. They are at a distance of 1600 and 820 light years from Earth. Another bright star in the Northern hemisphere, Betelgeuse is also located in the constellation of Orion. It emits 22,000 times more light than the Sun.
Most bright stars in the Northern hemisphere can be seen in the constellation of Orion.
Sirius of the constellation Canis major is the brightest star seen from the Earth. It can be observed in the southern hemisphere. Sirius brighter than the Sun is only 22.5 times, but the distance to this star by cosmic standards small is 8.6 light years. Polar star in the constellation URSA Minor shines as 6000 Suns, but she is removed from us at 780 light years, so looks like the dimmer is close to Sirius.
In the constellation of Taurus is a star with an astronomical name UW AGR. It can be seen only through a telescope. It is a blue giant star is different density and a small spherical size. It shines in the 860,000 times brighter than the Sun. This is a unique heavenly body is considered to be the brightest object in the observable Universe.
Advice 2: Which star appears first
Starry sky is fascinating. It impressed people with their splendor since time immemorial. Knowing that the Earth is only a grain of sand the Universe, stops the heart. How many stars in the sky, no one will be able to say with certainty, you can only know which star appears first.
The first bright point in the evening sky Venus appears, though this is not a star. If you want to see it, just after sunset look to the West. Of course, it all depends on weather conditions and time of year, but most often the first to observe that is Venus. It is the second planet from the Sun, some call it the "evening star". Even after a night out on the background of other stars, she pretty clearly stands out, it's hard to miss. However, to observe Venus can be long, only a couple of hours, to the middle of the night she seemed to disappear. Few people know that Venus can be called "the morning star", because there are times when all the stars have gone out, and that the bright point continues to glow on a background of dawn. People sang Venus since time immemorial, worshipped her, praised in poems, portrayed on the canvas. Yes, Venus - planet, but for many, even today, as in ancient times, it remains the "evening star".
Of all the stars brighter for us all shines Sirius, which is why it can be seen before the other in the evening sky. The fact that Sirius is very close to the Ground, of course, if you talk on a cosmic scale. The distance from planet Earth to the legendary star - just nine light years. However, in reality, Sirius is an ordinary star no different from the others. Only because of the small distance of Sirius, it seems magnificent bright giant compared to other, more distant stars.
Many believe that the brightest star Sirius, and the Arctic. If we talk about the visual effect they produce in the ordinary observation of a starry sky, then it is safe to say that Sirius is superior to the Polar star by its brightness. However, you should know that Sirius is actually the Polar star and sloppy.
The fact is that the North star is a supergiant. It is several times heavier and ten times more than the Sun, scientists have calculated that it is two thousand times brighter than his. North star far from Earth, so it is impossible for the naked eye to see its greatness. To an ordinary observer it is just a tiny dot in the sky. The distance from the Earth to this giant is 431 light year, which is ten times the distance of Sirius.
The perception of brightness of stellar objects may be different. It all depends on weather conditions and time of year.