?Ophiuchus is one of the thirteen constellations that cross the ecliptic.[65] It has sometimes been suggested as the "13th sign of the zodiac". However, this confuses zodiac or astrological signs with constellations.[66] The signs of the zodiac are a twelve-fold division of the ecliptic, so that each sign spans 30° of celestial longitude, approximately the distance the Sun travels in a month, and (in the Western tradition) are aligned with the seasons so that the March equinox always falls on the boundary between Pisces and Aries.[67][68] Constellations, on the other hand, are unequal in size and are based on the positions of the stars. The constellations of the zodiac have only a loose association with the signs of the zodiac, and do not in general coincide with them.[69] In Western astrology the constellation of Aquarius, for example, largely corresponds to the sign of Pisces. Similarly, the constellation of Ophiuchus occupies most (29 November – 18 December[70]) of the sign of Sagittarius (23 November – 21 December). The differences are due to the fact that the time of year that the Sun passes through a particular zodiac constellation's position has slowly changed (because of the precession of the Earth's rotational axis) over the centuries from when the Babylonians originally developed the Zodiac.[71][72]

The link does explain it, and if you listened to fundamental Christians describe their beliefs, you’d understand them better. You don’t have to agree, but if you never have an open mind even to things you disagree with you will never understand them.