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In process of increase in number of studied stars it became impossible to remember their names, and since 1603 rather bright stars in constellations began to designate letters of the Greek alphabet, as a rule, in decreasing order of shine of stars.

Much later for designations of stars have entered digital numbering on the constellations, nowadays, as a rule, applied only for weak stars which in a number of constellations are designated also by letters of the Latin alphabet. Designations of stars are put down on modern star charts and in special lists of the stars called by star catalogues. By this time astronomers have registered in star catalogues all stars, visible with the naked eye, and also many stars accessible to supervision only in telescopes. Census of stars shows that to a naked eye are accessible to supervision in all sky about five and a half thousand stars, and in territory of Russia it is visible only about three thousand. Other set of stars because of their weak shine is inaccessible to a naked eye.

Gradual detailed elaboration in studying of stars has led to necessity to enter their quantitative estimation to "visible brightness" or as now it is accepted to name more to pravil th, their shine. That stars have various shine, it is visible already at the first, even the fluent review of the star sky: one of them are very bright and at once draw attention of the observer, others are less bright, and not so are evident, the third are so weak that are not visible with open years and for their supervision optical tools are required. Precisely to define shine of stars, it is necessary to enter a certain numerical scale. It would be possible to measure quantity of light which reaches from a star the observer (to the Earth), in the usual units of light energy applied in the physicist. However the similar system of an estimation of shine of stars would be almost inconvenient for two reasons:

First, the quantity of light reaching from stars us so it is insignificant is not enough that measurement by its standard physical units would be like measurement of the sizes of details of the mechanism of a watch in kilometres;

Secondly, the gradation of shine of stars accepted in this case would be so is great that the shine scale would appear extraordinary bulky and it would be impossible to remember values of shine even the brightest stars.

Therefore shine of stars is expressed not in absolute physical (or lighting) units, and in the special conditional scale entered still in II century B. C. by Ancient Greek astronomer Gipparhom (180 110 BC) when was not and in помине physical units of measurements of light energy. This scale is called as a scale of star sizes. The name of a scale, maybe, and not absolutely successfully as the scale does not estimate the linear sizes of stars but only shine of stars allows to compare with each other. Presently the scale of star sizes considerably is improved and for definition of shine of stars the exact optical equipment is used.

If the beginning fan of astronomy asks, as it is possible to estimate shine of stars in a conditional scale, let he will recollect temperature measurement. After all the temperature is the certain physical characteristic, and it is measured in the conditional scale named a scale of degrees.

In astronomy there is a number of scales of star sizes which are applied depending on research objectives. So, for last 30 years photo-electric methods of studying of shine of stars by means of photo cells which under the influence of light generate an electric current (photocurrent) - the phenomenon opened still in 1888-1890 by the Russian physicist And have widely taken root. G. Stoletovym (1839-1896). Modern sensitive photo cells give a weak electric current under influence is insignificant small illumination, but special devices strengthen a current to the size accessible to measurement with the big accuracy.

Research of radiation of stars in different beams allows to receive a number of the important physical characteristics of stars. For this purpose also define shine of stars in different beams for what before photo cells put optical filters of different colour.

Now, when we have got acquainted with measurement of shine of stars, it is curious to notice that not too it is a lot of very bright stars of zero and first star size, only 24 in all sky, but weak - billions! This results from the fact that shine of stars depends not only on their valid luminosity, but also from distances: the further from us there are stars, the more poorly they look. Colour of stars depends on their superficial temperature.

In total in sky northern hemisphere is about 2900 stars, visible with the naked eye, i. e. To 6.

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