Ophiuchus, the constellation that the astrologers chose to ignore | Science &

In January 1995, Jacqueline Mitton, from the British Royal Astronomical Society, announced in a BBC show that the 12 signs of the zodiac were not only erroneously advanced due to the effects of precession of the Earth, but that they were, in fact, 13. Mitton explained that the ecliptic (the Sun’s apparent annual journey through the heavens) passes through a thirteenth constellation: Ophiuchus – the Latin version of Asclepius, the Greek god of medicine. The ecliptic had actually always passed through that constellation, although the dates change with the centuries.

The astrologers, baffled, faced a problem: how to integrate this constellation as a sign of the zodiac.

To explain this astral blunder, we first have to clarify that a constellation is an “apparent” grouping of stars: they seem to be on the same plane, but they are actually at different distances and are not necessarily related to each other. By agreement, today it is each of the 88 areas in which the sky is divided, as well as the group of stars they contain. However, throughout history – beginning in Mesopotamia – the total number of constellations and the area they occupied varied, depending on the person who cataloged the stars. Then, between 1922 and 1930, the constellations were definitively established by the International Astronomical Union (IAU).

The astronomical zodiac is an imaginary belt that is distributed along the celestial equator and on which are located the 12 ancient constellations, of different sizes, designated with the names of the figures that their shapes inspired: a ram, a bull, Sagittarius the archer and so on. Ophiuchus – which Greek astronomer Ptolemy included among the 48 constellations of his treatise the Almagest – was probably not taken into account because, aside from the aversion to the number 13, dividing the 360-degree zodiacal band among 13 constellations would not have produced an exact number.

Meanwhile, the astrological zodiac is divided into 12 equal, 30-degree portions, each corresponding to a sign: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.

It was the Greek astronomer Hipparchus of Nicaea who, in the 2nd century BC, deduced that the Celestial Sphere had a retrograde motion, which he called precession. Due to the gravitational influence of the other bodies in the Solar System and the roundness of our planet, the Earth behaves like a spinning top in such a way that the relative positions of the stars with respect to the equator and the poles vary throughout a 26,000-year cycle, in which the Earth makes a complete revolution around the axis of the ecliptic.

However, the vindication of Ophiuchus as a zodiacal constellation between Scorpio and Sagittarius is not due to the precession, which only affects dates, but to the tracing of the classic celestial map and, above all, to the arbitrary division of the sky into constellations done by the IAU. Its name derives from Greek and means “he who holds the serpent.” This constellation is represented by the figure of Asclepius, who holds a snake in his hands, with its head facing west and its tail east.

Ophiuchus continues…