About stars.

Each star in the sky is an enormous glowing ball of gas. The stars surface temperature varies. Some stars may have the temperature of 30,000 K, while the others are of only 3,000 K. The temperature of our Sun's surface is about 6,000K. The star surface implies only visible surface as gas ball lack any solid surface at all. As a rule the stars are much larger in size than planets and above all they are of greater stellar mass. In the Universe there are somewhat strange stars with the size typical for planets though exceeding planets many times by their mass. The Sun stellar mass is 750 times more than masses of other celestial bodies of Solar system. There are stars with the size hundred times more than that of the Sun and their masses hundred times less than solar masses. However here the stellar mass is subject to certain limits, i.e. from one twelfth of the Sun's mass up to 100 of solar masses. There may exist stars with a greater mass but such stars are very rare, indeed. It is easy to guess upon reading the last lines that stars differ much as to their stellar density. Among them there are stars with the matter cubic centimeter overweighing big loaded ocean-going vessel. Other stars' matter is so rarefied that its density is less than the density of optimal vacuum obtainable under earthy laboratory conditions.

Even for the light emitted by the nearest stars it takes several years to reach the Earth while the stars themselves look just like small dots through the most powerful telescopes. The said picture is not exactly correct though, i.e. the stars do look like tiny discs, which is rather the result of the distortions concerning telescopes than the magnification effect. There are thousands upon thousands stars. Nobody can come up with their exact number, at that one should take in regard the astration process and the defunct stars for the stars are born and die as a matter of fact. One can only state that in our Galaxy there exist about 150,000,000,000 stars and in the Universe there is an unidentified number of billions of galaxies… At the same time the number of lucid stars is more or less definite, i.e. about 4.5 thousand. Moreover, within the set limits of stars brightness that are accessible to human eye this number may be calculated within the accuracy. Bright stars have been countered and registered accordingly in the catalogs long time ago. The star brightness (or it is also called luminosity) is characterized with the star magnitude that astronomers have long ago mastered to determine.