The stars that can be seen on a clear night form certain figures that we call "constellations", and that serve to more easily locate the position of the stars.
In total, there are 88 groups of stars that appear in the celestial sphere and that take their name from religious or mythological figures, animals or objects. The term constellation it also refers to a delimited area of the celestial sphere that comprises the groups of named stars.
The oldest known constellation drawings indicate that they had already been established around 4000 B.C. The Sumerians gave the name to the constellation Aquarius, in honor of their god An, who spills the water of immortality on Earth. The Babylonians had already divided the zodiac into 12 equal signs by 450 B.C.
The current constellations of the northern hemisphere differ little from those known to the Chaldeans and the ancient Egyptians. Homer and Hesiod mentioned these figures and the Greek poet Arato de Soli gave a verse description of 44 constellations in his Phaenomena. Ptolemy, astronomer and Greek mathematician, in Almagesto, described 48 constellations, of which 47 are still known by the same name.
Many other cultures grouped the stars into figures, although they do not always correspond to those of the West. However, some Chinese constellations resemble western ones, which leads us to think about the possibility of a common origin.
At the end of the 16th century, the first European explorers of the South Seas drew maps of the southern hemisphere. Dutch navigator Pieter Dirckz Keyser, who participated in the exploration of the East Indies in 1595 added new constellations. Later, other figures from the southern hemisphere were added by German astronomer Johann Bayer, who published the first extensive celestial atlas.
Throughout history there were those who proposed new constellations, but astronomers finally agreed on a list of 88. However, their limits remained the subject of discussion until 1930, when the International Astronomical Union set those limits.
To designate the approximately 1,300 bright stars, the genitive of the constellation name is used, preceded by a Greek letter; This system was introduced by Johann Bayer. For example, the famous star Algol, in the constellation Perseus, is called Beta Persei.
The constellations of the Zodiac
Among the best known are those found in the plane of the Earth's orbit on the background of the fixed stars. Are the constellations of the zodiac. In addition to these, some well known are Cruz del Sur, visible from the southern hemisphere, and Ursa Major, visible from the northern hemisphere. These and others allow locating the position of important reference points such as, for example, the celestial poles.
Although the zodiac is usually divided into twelve constellations, corresponding to the 12 signs, the ecliptic of the Earth passes through thirteen figures in the sky. Missing Ophiuchus, the snake hunter or Serpentarium. Therefore, the circle of the complete zodiac would be: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Ophiuchus, Sagittarius, Capricorn, Aquarius and Pisces.
The largest constellation of the celestial sphere is that of Hydra, which contains 68 stars visible to the naked eye. The Southern Cross (Crux) in the southern hemisphere is the smallest. These two constellations are not in the zodiac.
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