How to find the approached position of heavenly equator, we will show slightly more low, and now we will notice that in territory of Soviet Union all constellations of northern hemisphere of the sky and some constellations of southern hemisphere, depending on geographical width of a place of supervision are visible: the it is located to the south, the it is more than southern hemisphere constellations is accessible to supervision. So, in Leningrad the part of stars of southern constellation of the Scorpion is visible only and that is very low over horizon, and the Centaur constellation is completely not visible. In Armenia, Georgia and Uzbekistan already many stars of constellation of a Centaur and all constellation of the Scorpion are visible.
Not all constellations can be found at once in the sky as many of them consist of weak stars, and only about 30 constellations are accurately allocated with the contours and bright stars. Constellations of the Big Dipper, Pegasa, Kassiopei, Voznichego, the Lion concern them and others. The areas occupied with constellations in the sky, and number of stars in them far are not identical. By the way, we will notice that distances between visible positions of stars in the sky are measured in degrees, minutes and seconds of an arch, and the areas occupied with constellations in the sky, - in square degrees. From bright constellations the greatest on the area is the constellation of the Big Dipper occupying the space in 1280 square degrees and numbering, besides seven bright stars of a ladle, 118 more stars, visible with the naked eye. The most small constellation is in southern hemisphere of the sky and it is not visible in territory of Russia is a beautiful bright constellation of the Southern Cross, the area in 68 square degrees, consisting of five bright and weaker 25 stars. The smallest constellation of northern sky usually do not know, as it consists only of 10 weak stars visible with the naked eye; it is called as constellation of the Small Horse, has the area in 72 square degrees and adjoins southwest border of constellation of Pegasa.
Most of all bright stars, namely 12, contains constellation of the Scorpion, but, perhaps, the most beautiful constellation of all sky is already mentioned constellation of Orion numbering 120 stars, visible with the naked eye among which seven are allocated with the shine.
In each constellation the basic stars have those or other designations. In the ancient time own names, many of which, mainly Greek and Arabian were given to the brightest stars of each constellation, have reached up to now. So, seven bright stars of a ladle of the Big Dipper have received names: Dubhe, Merak, Fekda, Megrets, Aliot, Mitsar and Benetnash. p> 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;
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