Today we want to talk to you about an extremely interesting topic;what are stars and their characteristics. So read carefully and don't miss any details, we assure you that you will love this theme.
What are stars?
A star? It's all those things that shine at night! Yes, of course, but… can we define them?
Everyone knows about stars, but it's not necessarily easy to describe their properties, and besides, we haven't known for long what a star is.
Thousands of hypotheses have been proposed over the centuries, see which are the best known:
In the 5th century BC, Anaxagoras thought the Sun was a shiny rock.
In the fourth century before Christ, Aristotle thought that the matter of the Earth was composed of the 4 elements (Earth, Air, Water and Fire) but that the celestial bodies or stars were composed of many more elements.
Our vision is not sharp enough to discover the incredible complexity of the stars that shine in the celestial vault. Especially since we only have access to visible light, while stars emit radiation across the entire range of the electromagnetic spectrum.
From ultra energetic gamma rays, to long radio waves. And that high-energy radiation is stopped by our atmosphere. That is why properly defining what a star is can be a somewhat complex task.
The stars, classification and their colors
We know that the Sun is a medium-sized and bright star, compared to other stars in our galaxy. The classification of stars is carried out according to two parameters: surface temperature and luminosity.
If we plot the stars on a graph that gives luminosity as a function of surface temperature, we see that the stars are not evenly distributed. This graph is called the HR diagram, after the astronomers Hertzsprung and Russel who made this discovery.
Most stars are grouped in a diagonal stripe. This reflects the link between a star's surface temperature and its luminosity; a hotter star is brighter. The color of the star is also directly related to its temperature, a hot star is blue and a cool star is red.
The intensity of the spectral lines also varies with temperature. We define spectral type as follows: O, B, A, F, G, K, M. O and B stars are hot, M stars are cool. The Sun is a yellow star, spectral type G.
Brightness of the stars
The luminosity also depends on the size of a star. Stars on the HR diagram are systematically brighter than main sequence stars of the same temperature, because they are larger. These represent only a small percentage of stars, but are several thousand times brighter than the Sun. They are the dominant among the stars visible to the naked eye.