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People in many cultures have imagined that the brightest stars form constellations, which are apparent pictures in the sky seeming to be persistent, being deemed also as fixed. That way, constellations have been used for centuries, and still are today, to identify regions of the night sky by both professional and amateur astronomers.
Some of the Northern Sky's former constellations were placed in the less populated regions between the traditional brighter constellations just to fill gaps. In the Southern Sky, new constellations were often created from about the 15th century by voyagers who began journeying south of the Equator. European countries like England, France, the ...
Constellation positions change throughout the year due to night on Earth occurring at gradually different portions of its orbit around the Sun. As Earth rotates toward the east, the celestial sphere appears to rotate west, with stars circling counterclockwise around the northern pole star and clockwise around the southern pole star.
Such measurements show no shifts in the stars' positions. Unlike the Sun, Moon, and planets, they do not change position with respect to one another over human lifetimes; the shapes of the constellations are constant. This makes them a convenient reference background for determining the shape of Earth.
Because of precession, the positions of the constellations slowly change over time. By comparing the positions of the 41 constellations against the grid circles, an accurate determination can be made of the epoch when the original observations were performed. Based upon this information, the constellations were catalogued at 125 ± 55 BC.
In a given constellation, the first variable stars discovered were designated with letters R through Z, e.g. R Andromedae. This system of nomenclature was developed by Friedrich W. Argelander, who gave the first previously unnamed variable in a constellation the letter R, the first letter not used by Bayer.
Further, the creation of the zodiac and the disconnect from the constellations was because the sun is not in each constellation for the same amount of time. [26]: 25 This disconnection from the constellations led to the problem with precession separating the zodiac symbols from the constellations that they once were related to.
Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution