A constellation is a group of stars in the celestial sphere that close enough gave the imaginary appearance of a figure on the celestial vault. A constellation is an particular asterism astronomy, astronomy, an asterism is a remarkable figure drawn by stars particularly bright. . In the sky, the stars of a constellation are very distant from each other but appear grouped into figures, so that the constellation has no proper distance. Western constellations are grouped into two parts, dividing the sky more or less in the two hemispheres, the austral sky to the south and the boreal sky to the north. The boreal constellations are the oldest and correspond to plane of sky visible from regions of the Mediterranean by the ancient astronomers.
The southern constellations were named by western astronomers after the fifteenth century. The International Astronomical Union (IAU) divides the sky into 88 constellations official with precise boundaries, so that each point in the sky belongs to a constellation. Man is fascinated by this cosmic scene that represents the sky observed without any artificial lighting. The stars all seem to hang at the same distance from the earth. The sky changes day and night throughout the year. At first sight the sky is dotted with thousands of bright and glitter stars.
In theory, you could see a single glance about 3800 stars in reality only about 2600 are visible due to stray light. It is the rotation of the Earth creates the horizon bisecting the celestial sphere. To the pole, all the stars revolve around the zenith, in parallel to the horizon. At the equator all the stars rise and set, the celestial poles are on the horizon. Therefore, all the stars from one pole to the other are visible at certain moments of the year. At midlatitudes some stars are circumpolar A celestial object (typically a star) is called circumpolar compared to an observation given if it is visible at all periods of the year. In the northern hemisphere, a star disappears below the horizon when the sum of its declination and latitude the place of observation is smaller than 90 °. The notion of 'circumpolar' is linked to the place of observation. Thus, to the North Pole all positive declination stars are circumpolar, so there is no circumpolar star at the equator. A constellation is said circumpolar, if all of its main stars are circumpolar. or always above the horizon while others wake up and lie down.